#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

int solve() {
  ll 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) return -1;
  n /= g, m /= g, mod /= g;
  auto [gx, x] = internal::inv_gcd(n, mod);
  assert(gx == 1);
  int k = (ll)m * x % mod;
  if (k == 0) k = mod;
  return k;
}

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int tt;
  cin >> tt;
  while (tt--) {
    cout << solve() << '\n';
  }
}