#include <bits/stdc++.h>
using namespace std;

#define rep(i, N) for (int i = 0; i < (int)N; i++)

int main() {
  int T;
  cin >> T;
  rep(i, T) {
    int A, B;
    cin >> A >> B;
    int k = B / A;
    int X = -1;
    while (k > 0) {
      if (k == 1) {
	if (A == B)
	  X = 0;
	break;
      }
      if ((B - k*A) % (k-1) == 0) {
	X = (B - k*A) / (k-1);
	break;
      }
      k--;
    }
    cout << X << endl;
  }
  return 0;
}