#include <bits/stdc++.h>

using namespace std;

void fast_io() {
	ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
}

pair<long long, long long> extended_gcd(long long a, long long b) {
	if (b == 0) {
		return {1, 0};
	}
	auto [x, y] = extended_gcd(b, a % b);
	return {y, x - a / b * y};
}
void solve() {
	long long n, m;
	cin >> n >> m;
	long long mod = 1e9;
	m = (mod - m % mod) % mod;
	long long g = gcd(n, mod);
	if (m % g) {
		cout << -1 << '\n';
		return;
	}
	// min natural number x such that n * x % mod == m
	n /= g;
	m /= g;
	mod /= g;
	auto [x, y] = extended_gcd(n, mod);
	x = (x * m % mod + mod) % mod;
	if (x == 0) x += mod;

	cout << x << "\n";
}
int main() {
	fast_io();
	int t;
	cin >> t;
	for (; t--;) {
		solve();
	}
}