#ifndef ELSIE_LOCAL_H
#define ELSIE_LOCAL_H
#ifndef ELSIE_MISC_HEADER
#define ELSIE_MISC_HEADER
#if __has_include(<atcoder/modint>)
#include "atcoder/modint"
using namespace atcoder;
using mint=modint998244353;
using mint1=modint1000000007;
#endif
#include <limits>
#include <new>
#include <initializer_list>
#include <compare>
#include <concepts>
#include <utility>
#include <bitset>
#include <tuple>
#include <type_traits>
#include <functional>
#include <chrono>
#include <array>
#include <deque>
#include <list>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <iterator>
#include <ranges>
#include <algorithm>
#include <bit>
#include <random>
#include <numeric>
#include <numbers>
#include <iostream>
#include <ios>
#include <streambuf>
#include <iomanip>
#include <sstream>
#include <regex>
#include <cassert>
#include <cctype>
#include <climits>
#include <cmath>
#include <cstdarg>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
using namespace std;
using namespace chrono;
using std::cin;
using std::cout;
using sstream=stringstream;
#endif
#ifndef ELSIE_MISC_DEFINE
#define ELSIE_MISC_DEFINE
#define RET return
#define fi first
#define se second
#define endl '\n'
#define sn(i,c) " \n"[i==c]
#define rsv(n) reserve(n)
#define pf(a) push_front(a)
#define pb(a) push_back(a)
#define eb(...) emplace_back(__VA_ARGS__)
#define ppf() pop_front()
#define ppb() pop_back()
#define pp() pop()
#define ins(a) insert(a)
#define emp(...) emplace(__VA_ARGS__)
#define ers(a) erase(a)
#define cont(a) contains(a)
#define mp(f,s) make_pair(f,s)
#define A(a) begin(a),end(a)
#define I(a,i) begin(a),begin(a)+(i)
#define _SEL4(_1,_2,_3,_4,name,...) name
#define _SEL3(_1,_2,_3,name,...) name
#define _REP4(i,s,n,st) for(long i=(s);i<(n);i+=(st))
#define _REP3(i,s,n) _REP4(i,s,n,1)
#define _REP2(i,n) _REP3(i,0,n)
#define _REP1(n) _REP2(_,n)
#define _RREP4(i,n,t,s) for(long i=(n);i>=(t);i-=(s))
#define _RREP3(i,n,t) _RREP4(i,n,t,1)
#define _RREP2(i,n) _RREP3(i,n,0)
#define _ITER2(x,a) for(auto&&x:a)
#define _ITER3(x,y,a) for(auto&&[x,y]:a)
#define _CTER2(x,a) for(const auto&x:a)
#define _CTER3(x,y,a) for(const auto&[x,y]:a)
#define rep(...) _SEL4(__VA_ARGS__,_REP4,_REP3,_REP2,_REP1)(__VA_ARGS__)
#define rrep(...) _SEL4(__VA_ARGS__,_RREP4,_RREP3,_RREP2,_REP1)(__VA_ARGS__)
#define iter(...) _SEL3(__VA_ARGS__,_ITER3,_ITER2)(__VA_ARGS__)
#define cter(...) _SEL3(__VA_ARGS__,_CTER3,_CTER2)(__VA_ARGS__)
#endif
#ifndef ELSIE_MISC_CONST
#define ELSIE_MISC_CONST
#define NL cout<<'\n'
#define npi numbers::pi
constexpr int64_t inf=1ll<<60,minf=-inf;
constexpr int32_t inf32=1ll<<30,minf32=-inf32;
constexpr char sep='\n';
constexpr array<pair<int32_t,int32_t>,8>dc={{{1,0},{0,1},{-1,0},{0,-1},{1,1},{1,-1},{-1,1},{-1,-1}}};
#define yes cout<<"Yes\n"
#define no cout<<"No\n"
#define yn(c) (c)?yes:no
#endif
#if __cplusplus > 202002L
#ifndef ELSIE_MISC_FUNC
#define ELSIE_MISC_FUNC

namespace vies=std::views;
#define DR(i) views::drop(i)
#define TK(i) views::take(i)
#define RV views::reverse
#define IOTA vies::iota

#define rev(a) reverse(A(a))
#define minel(a) min_element(A(a))
#define maxel(a) max_element(A(a))
#define acm(a) accumulate(A(a),0ll)
#define nxpm(a) next_permutation(A(a))
#define Sort(a) sort(A(a))
#define uni(a) Sort(a);a.erase(unique(A(a)),a.end())
#define swapcase(a) a=(isalpha(a)?a^32:a)

template<class T,class U>inline void chmax(T&a,const U&b){if(a<b)a=b;}
template<class T,class U>inline void chmin(T&a,const U&b){if(a>b)a=b;}


#define _BISECT4(_1,_2,_3,_4,name,...) name
#define _LB_BEX(b,e,x) lower_bound(b,e,x)
#define _LB_BEXG(b,e,x,g) lower_bound(b,e,x,g)
#define _UB_BEX(b,e,x) upper_bound(b,e,x)
#define _UB_BEXG(b,e,x,g) upper_bound(b,e,x,g)
#define lb(...) _BISECT4(__VA_ARGS__,_LB_BEXG,_LB_BEX)(__VA_ARGS__)
#define ub(...) _BISECT4(__VA_ARGS__,_UB_BEXG,_UB_BEX)(__VA_ARGS__)

#define TP template<class T,class U,typename cp=less<U>>
template<class T,class U>concept LUBI= same_as<T,vector<U>>||same_as<T,deque<U>>||is_array_v<T>;
#define RL requires LUBI<T,U>

TP size_t lbi(const T&v,const U&x,cp cmp=cp())RL{RET lb(A(v),x,cmp)-begin(v);}
TP size_t ubi(const T&v,const U&x,cp cmp=cp())RL{RET ub(A(v),x,cmp)-begin(v);}
TP size_t lbi(size_t i,const T&v,const U&x,cp cmp=cp())RL{RET lb(i+A(v),x,cmp)-begin(v);}
TP size_t ubi(size_t i,const T&v,const U&x,cp cmp=cp())RL{RET ub(i+A(v),x,cmp)-begin(v);}
TP size_t lbi(const T&v,size_t i,const U&x,cp cmp=cp())RL{RET lb(I(v,i),x,cmp)-begin(v);}
TP size_t ubi(const T&v,size_t i,const U&x,cp cmp=cp())RL{RET ub(I(v,i),x,cmp)-begin(v);}
TP size_t lbi(size_t i,const T&v,size_t e,const U&x,cp cmp=cp())RL{RET lb(i+I(v,e),x,cmp)-begin(v);}
TP size_t ubi(size_t i,const T&v,size_t e,const U&x,cp cmp=cp())RL{RET ub(i+I(v,e),x,cmp)-begin(v);}

#undef TP
#undef RL
#define TP template<integral T>
#define MT make_unsigned_t<T>

TP constexpr int32_t pcnt(T p){return popcount(MT(p));}
TP constexpr int32_t lsb(T p){return countr_zero(MT(p));}
TP constexpr int32_t msb(T p){return sizeof(T)*8-1-countl_zero(MT(p));}

template<int32_t N,integral T>
void putbit(T s){
    char buf[N+1]={0};
    for(char*itr=buf+N-1;itr>=buf;itr--,s>>=1)
        *itr='0'+(s&1);
    cout<<buf<<sep;
}
#undef TP
#undef MT
#endif
#ifndef ELSIE_STD_IO
#define ELSIE_STD_IO

#define INT(...) int __VA_ARGS__;in(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__;in(__VA_ARGS__)
#define STR(...) str __VA_ARGS__;in(__VA_ARGS__)
#define VI(a,n) vi a(n);in(a)
#define VIT(a,n) vit a(n);in(a)
#define VS(a,n) vs a(n);in(a)
#define UV(u,v) INT(u,v);--u,--v
#define UVW(u,v,w) INT(u,v,w);--u,--v
#ifdef LOCAL
#define dput(...) dos=&cerr;out(__VA_ARGS__);dos=&cout
#else
#define dput(...)
#endif

template<class T>concept Lint=same_as<T,__int128_t>||same_as<T,__uint128_t>;
template<class T>concept Itrabl=requires(const T&x){x.begin();x.end();}&&!std::is_same_v<T,string>;
template<class T>concept IItrabl=Itrabl<T>&&Itrabl<typename T::value_type>;
template<class T>concept ModInt=requires(const T&x){x.val();};
template<class T>concept NLobj=Itrabl<T>||std::is_same_v<T,string>;

istream&operator<<(istream&is,__float128&x){double y;is>>y;x=y;return is;}
ostream&operator<<(ostream&os,const __float128&x){return os<<static_cast<double>(x);}

template<Lint T>ostream&operator<<(ostream&dst,T val){
    ostream::sentry s(dst);
    if(!s)return dst;
    char _O128[64];
    char*d=end(_O128);
    bool vsign=val<0;
    __uint128_t v=val;
    if(vsign&&val!=numeric_limits<T>::min())v=1+~(__uint128_t)val;
    do{
        *(--d)="0123456789"[v%10];
        v/=10;
    }while(v!=0);
    if(vsign)*(--d)='-';
    ptrdiff_t len=end(_O128)-d;
    if(dst.rdbuf()->sputn(d,len)!=len)dst.setstate(ios_base::badbit);
    return dst;
}

template<Lint T>istream&operator>>(istream&src,T&val) {
    string s;src>>s;
    bool is_neg=numeric_limits<T>::is_signed&&s.size()>0&&s[0]=='-';
    for(val=0;const auto&x:s|views::drop(is_neg))val=10*val+x-'0';
    if(is_neg)val*=-1;
    return src;
}

template<ModInt T>istream&operator>>(istream&is,T&v){int64_t x;is>>x;v=x;return is;}
template<class T,class U>istream&operator>>(istream&is,pair<T,U>&v){return is>>v.first>>v.second;}
template<Itrabl T>istream&operator>>(istream&is,T&v){for(auto&&x:v)is>>x;return is;}

template<class T>void in(T&a){cin>>a;}
template<class T,class... Ts>void in(T&a,Ts&... b){in(a);in(b...);}

template<class T,class U>vector<pair<T,U>>zip(size_t n,size_t m){
    vector<pair<T,U>>r(min(n,m));
    iter(x,y,r)in(x);
    iter(x,y,r)in(y);
    return move(r);
}
template<class T,class U>vector<pair<T,U>>zip(size_t n){return move(zip<T,U>(n,n));}

template<ModInt T>ostream&operator<<(ostream&os,const T&v){return os<<v.val(); }
template<class T,class U>ostream&operator<<(ostream&os,const pair<T,U>&v){return os<<'('<<v.first<<','<<v.second<<')';}
template<Itrabl T>ostream&operator<<(ostream&os,const T&v){size_t cnt=0;cter(x,v)os<<x<<(++cnt<v.size()?" ":"");return os;}
template<IItrabl T>ostream&operator<<(ostream&os,const T&v){size_t cnt=0;cter(x,v)os<<x<<(++cnt<v.size()?"\n":"");return os;}
inline ostream*dos=&cout;
inline int32_t OFLG; // 0:first, 1:notNLobj, 2:NLobj
template<class T>void _out(const T&a){if(OFLG)(*dos)<<"0 \n"[OFLG]<<a;else(*dos)<<a;OFLG=1;}
template<NLobj T>void _out(const T&a){(*dos)<<(OFLG?"\n":"")<<a;OFLG=2;}
template<class T,class...Ts>void _out(const T&a,const Ts&... b){_out(a);_out(b...);}
template<class... Ts>void out(const Ts&... v){OFLG=0;_out(v...);(*dos)<<sep;}
#endif
#endif
#endif
#ifndef ELSIE_BASIC_MATH
#define ELSIE_BASIC_MATH
namespace elsie{
using namespace std;
using namespace atcoder;

template<integral T,integral U>
inline auto ceil(const T a,const U b){return(a+b-1)/b;}
template<integral T,integral U>
inline auto floor(const T a,const U b){return a/b-(a%b&&(a^b)<0);}

// std::ceil(std::sqrtl(x:u64))が64bit精度で40%高速なので，long double 80bitならそちらを使うべき
template<bool internal_invocate=false>
inline uint64_t sqrt_ceil(uint64_t x){
    if constexpr(!internal_invocate){
        // sqrt_floorからの呼出しではここをスキップする
        if(x>uint64_t(UINT32_MAX)*UINT32_MAX)return 1ull<<32;
        else if(x<2)return x!=0;
    }
    uint64_t nx,y=min<uint64_t>((1ULL<<((64-countl_zero(x))>>1)+1)-1,UINT32_MAX);
    y-=(y*y-x)/(y<<1);
    y-=(y*y-x)/(y<<1);
    y-=(y*y-x)/(y<<1);
    y-=(y*y-x)/(y<<1);
    y-=(y*y-x)/(y<<1);
    nx=y-(y*y-x)/(y<<1);
    while(nx!=y){
        y=nx;
        nx=y-(y*y-x)/(y<<1);
        if(nx==y)break;
    }
    return y+(y*y<x?1:(y-1)*(y-1)>=x?-1:0);
}
inline uint64_t sqrt_floor(uint64_t x){
    if((uint64_t)UINT32_MAX*UINT32_MAX<=x)return UINT32_MAX;
    else if(x<4)return x!=0;
    uint64_t y=sqrt_ceil<true>(x);
    return y-(y*y!=x);
}

using u128=__uint128_t;
using u64 = uint64_t;
inline __uint128_t mul64to128(u64 a,u64 b){
    u64 hi,lo;
    asm("mulq %3" :"=a"(lo),"=d"(hi):"a"(a),"r"(b));
    return((__uint128_t)(hi)<<64)+lo;
}
inline pair<u128,u128>mul128(u128 a,u128 b){
    constexpr static u128 Lfilter=0xFFFF'FFFF'FFFF'FFFFull;
    u64 x1=a>>64,x0=a&Lfilter;
    u64 y1=b>>64,y0=b&Lfilter;
    u128 z2=mul64to128(x1,y1),z1=mul64to128(x1,y0)+mul64to128(x0,y1),z0=mul64to128(x0,y0);
    u128 lower=z0+(z1<<64);
    return{z2+(z1>>64)+(lower<z0),lower};
}
inline u128 rem256(pair<u128,u128>x,u128 mod){
    u128 rem32=(u128(1)<<32)%mod;
    u128 rem64=rem32*rem32%mod;
    u128 rem128=rem64*rem64%mod;
    auto&&[a,b]=x;
    a%=mod,b%=mod;
    return(a*rem128%mod+b)%mod;
}

int64_t safepow(int64_t a,uint64_t b){
    int64_t ret=1,k=a;
    double check=1,kcheck=a;
    while(b){
        if(b&1){
            check*=k;
            if(check>INT64_MAX)return INT64_MAX;
            if(check<INT64_MIN)return INT64_MIN;
            ret*=k;
        }
        kcheck*=k;
        if(kcheck>INT64_MAX)return INT64_MAX;
        if(kcheck<INT64_MIN)return INT64_MIN;
        k*=k;
        b>>=1;
    }
    return ret;
}

template<integral T,class U=make_unsigned_t<T>>
constexpr T modpow(T a,U b,U mod){
    if constexpr(is_same_v<U,__uint128_t>){ // mod=2^64専用
        constexpr __uint128_t filter=uint64_t(-1);
        a%=mod;
        __uint128_t ret=1;
        if(a<0)a+=mod;
        while(b){
            ret=(b&1?ret*a&filter:ret);
            a=a*a&filter;
            b>>=1;
        }
        return uint64_t(ret&filter);
    }else{
        __int128_t k=a%mod,ret=1;
        if(k<0)k+=mod;
        while(b){
            ret=(b&1?ret*k%mod:ret);
            k=(k*k)%mod;
            b>>=1;
        }
        return int64_t(ret);
    }
}

template<class S>S gcd(S a,S b){
    if(b==0) return a;
    S r=1;if(a<0)a=-a;if(b<0)b=-b;
    while(r) r=a%b,a=b,b=r;
    return a;
}

template<class S>S lcm(S a,S b){return a/gcd(a,b)*b;}

template<class S>S egcd(S a,S b,S&x,S&y){
    if(b==0){
        x=1,y=0;
        return a;
    }
    S d=egcd(b,a%b,y,x);
    y-=a/b*x;
    return d;
}

template<class T>T exgcd(T a,T b,T&x,T&y){
    auto assign=[&](T&s,T&t,T u,T v)->void {s=u,t=v;};
    x=1,y=0;
    T u=0,v=1;
    while(b){
        T k=a/b,r=a%b;
        assign(a,b,b,r);
        assign(x,u,u,x-u*k);
        assign(y,v,v,y-v*k);
    }
    if constexpr(is_signed_v<T>)
        if(a<0)a=-a,x=-x,y=-y;
    return a;
}

template<class T>T mod_inv(T a,T m){
    T x,y,g=exgcd(a,m,x,y);
    if(g!=1)return -1;
    return(x%m+m)%m;
}

template<class T>T mod_inv_prime(T a,T p){ return modpow(a,p-2,p); }

template<class mint=modint998244353>
class combination{
    private:
        using tint = long long;
        vector<mint>invprod,prod;
        vector<tint>inv;
        const unsigned long long M;
    public:
    combination(int64_t n=1):invprod(2,1),prod(2,1),inv(2,0),M(mint(-1).val()+1){
        inv[1]=1;
        if(n>1)PreCalc(n);
    }
    void PreCalc(int64_t n){
        size_t presize=inv.size();
        if(presize>=n+1)return;
        inv.resize(n+1);
        prod.resize(n+1);
        invprod.resize(n+1);
        for(int64_t i=presize;i<=n;++i){
            prod[i]=prod[i-1]*i;
            inv[i]=(((M/i)*(-inv[M%i]))+M)%M;
            invprod[i]=invprod[i-1]*inv[i];
        }
    }
    mint factorial(size_t n){
        PreCalc(n);
        return prod[n];
    }
    mint invfact(size_t n){
        PreCalc(n);
        return invprod[n];
    }
    mint P(size_t n,size_t k){
        if(n<k) return 0;
        PreCalc(n);
        return prod[n]*invprod[n-k];
    }
    mint C(size_t n,size_t k){
        if(n<k) return 0;
        PreCalc(n);
        return prod[n]*invprod[n-k]*invprod[k];
    }
    mint H(size_t n,size_t k){
        if(n==0) return mint(k!=0);
        PreCalc(n);
        return C(n+k-1,k);
    }
};

class barret32{
    uint64_t M,iM;
    public:
    barret32():M(0),iM(0){}
    barret32(uint32_t m):M(m),iM(uint64_t(-1)/m+1){}
    void set(uint32_t m){ M=m,iM=uint64_t(-1)/m+1; }
    uint32_t umod()const{ return M; }
    uint32_t mul(uint32_t a,uint32_t b)const{
        uint64_t z=(uint64_t)a*b;
        uint64_t x=((__uint128_t)z*iM>>64);
        uint64_t y=x*M;
        return(uint32_t)(z-y+(z<y?M:0));
    }
};

class barret64{
    __uint128_t M,iM;
    public:
    barret64():M(0),iM(0){}
    barret64(uint64_t m):M(m),iM(__uint128_t(-1)/M+1){}
    uint64_t umod(){ return M; }
    uint64_t mul(uint64_t a,uint64_t b){
        __uint128_t z=mul64to128(a,b);
        __uint128_t x=mul128(z,iM).first;
        __uint128_t y=x*M;
        return(uint64_t)(z-y+(z<y?M:0));
    }
};
}
#endif
#ifndef ELSIE_ALIAS
#define ELSIE_ALIAS

template<class f>using vc=vector<f>;
template<class f>using vv=vc<vc<f>>;
template<class f>using v3=vv<vc<f>>;
template<class f>using v4=vv<vv<f>>;

template<class f>using gr=greater<f>;
template<class f>using pq=priority_queue<f>;
template<class f>using pqg=priority_queue<f, vc<f>, gr<f>>;
#define uset unordered_set
#define umap unordered_map
using it=int32_t;
using i8=int8_t;   using u8=uint8_t;
using i16=int16_t; using u16=uint16_t;
using i32=int32_t; using u32=uint32_t;
using i64=int64_t; using u64=uint64_t;
using i128=__int128_t; using u128=__uint128_t;
using intw=__int128_t; using uintw=__uint128_t;
using f32=float;
using f64=double;
using f128=__float128;
using vi=vc<i64>;
using vit=vc<it>;
using vb=vc<bool>;
using pi=pair<i64,i64>;
using pit=pair<it,it>;
using str=string;
using vs=vc<str>;
using pqgp=pqg<pi>;
#define int i64
#define itn i64
#define LL long long
#endif

void slv(){
    constexpr int s=1'000'000'000;
    INT(n,m);
    n%=s;
    m%=s;
    if(m)m=s-m;
    if(n==0){
        if(m%s)out(-1);
        else out(1);
        return;
    }
    int k=elsie::mod_inv(n,s);
    if(k==-1&&m%n!=0) out(-1);
    else if(k!=-1)out(m*k);
    else out(m/n);
}

signed main(){
    cin.tie(0)->sync_with_stdio(0);
    cout<<fixed<<setprecision(15);
    INT(t);
    rep(t) slv();
}