#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int t; cin >> t;
	while (t--) {
		// nk + m == 0(mod 1e9)
		long long n, m; cin >> n >> m;
		int mod = 1e9;
		n %= mod;
		m %= mod;
		if (m)m = mod - m;
		int g = gcd(n, mod);
		if (m % g) {
			cout << -1 << endl;
			continue;
		}
		n /= g, m /= g, mod /= g;
		auto[gx, x] = internal::inv_gcd(n, mod);
		int ans = (long long)m * x %mod;
		if (ans == 0)ans = mod;
		cout << ans << endl;
	}
	return 0;
}