#include<bits/stdc++.h>
#include<atcoder/math>
using namespace std;
using ll=long long;
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
template<class T> bool chmax(T &a, T b){if (a < b){a = b;return true;} else return false;}
template<class T> bool chmin(T &a, T b){if (a > b){a = b;return true;} else return false;}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int T;
    cin>>T;
    while(T--){
        ll MOD=1'000'000'000;
        ll N,M;
        cin>>N>>M;
        N%=MOD;
        M%=MOD;
        if(N==0){
            if(M==0)cout<<1<<"\n";
            else cout<<-1<<"\n";
            continue;
        }
        ll g=gcd(N,MOD);
        if(M%g!=0)cout<<-1<<"\n";
        else{
            N/=g;
            M/=g;
            MOD/=g;
            ll inv=atcoder::inv_mod(N,MOD);
            ll ans=(inv*(MOD-M))%MOD;
            if(ans==0)ans+=MOD;
            cout<<ans<<"\n";
        }
    }
}