#include<bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;

#define all(v) v.begin(),v.end()
using ll = long long;
using ull = unsigned long long;
using lll = __int128;
using vll=vector<ll>;
using vvll = vector<vector<ll>>;
using P = pair<ll,ll>;
using vp=vector<pair<ll, ll>>;
//using mint=modint1000000007;
//using mint=modint998244353;

const ll INF=1ll<<60;
ll mod10=1e9+7;
ll mod99=998244353;
const double PI = acos(-1);

#define rep(i,n) for (ll i=0;i<n;++i)
#define per(i,n) for(ll i=n-1;i>=0;--i)
#define rep2(i,a,n) for (ll i=a;i<n;++i)
#define per2(i,a,n) for (ll i=a;i>=n;--i)

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }



long long exgcd(long long a,long long b,long long &x,long long &y){
    if(b==0){
        x=1;y=0;
        return a;
    }else{
        long long d=exgcd(b,a%b,y,x);
        y-=a/b*x;
        return d;
    }
}

pair<long long,long long> eq_solution(long long a,long long b,long long c){
    if(c%__gcd(a,b)!=0) return make_pair(INF,INF);
    ll x=0,y=0;
    exgcd(a,b,x,y);
    return make_pair(c/__gcd(a,b)*x,c/__gcd(a,b)*y);
}

ll mod_inv(ll a,ll m){
   auto [x,y]=eq_solution(a,m,1);
   
   return (x%m+m)%m;
}

bool solve(){
   ll a,b;cin>>a>>b;
   ll m=1e9;
   a%=m,b=(m-b%m)%m;
   if(a==0){
      cout << -1 << endl;
      return 0;
   }else if(b==0){
      cout << m << endl;
      return 0;
   }

   ll g=__gcd(a,m);
   if(b%g!=0){
      cout << -1 << endl;
      return 0;
   }
   a/=g,m/=g,b/=g;
   cout << mod_inv(a,m)*b%m << endl;
   return 0;
}





int main(){
   cin.tie(0);
   ios::sync_with_stdio(false);
   ll T=1;cin>>T;
   rep(i,T) solve();
}