#include<bits/stdc++.h>
using namespace std;
long long gcd_ext(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 = gcd_ext(b, a % b, y, x);
        y -= a / b * x;
        return d;
    }
}
long long inverse(long long a, long long P) { // aの逆元を求める
    long long x, y;
    gcd_ext(a, P, x, y);
    return (P + x % P) % P;
}
long long f(long long a, long long b, long long mod){
	long long inva = inverse(a, mod);
	cerr << b << " " << inva << " " << mod << " " << a*inva%mod << endl;
	return (b*inva)%mod;
}
void solve(){
	long long n, m;
	cin >> n >> m;
	long long mod = 1000000000;
	n %= mod;
	m = (mod - m%mod)%mod;
	long long g = __gcd(n, __gcd(m, mod));
	if((n == 0 && m != 0) || __gcd(n/g, mod/g) != 1){
		cout << -1 << endl;
		return;
	}
	n /= g;
	mod /= g;
	cerr << n << " " << m << " " << mod << endl;
	cout << f(n, m, mod) << endl;
	return;
}
int main(){
	int t;
	cin >> t;
	while(t--){
		solve();
	}
}