#pragma GCC optimize "O3,omit-frame-pointer,inline"
#pragma GCC push_options
#pragma GCC optimize ("unroll-loops")
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

signed main () {
  std::ios::sync_with_stdio(false); std::cin.tie(0);
  int t;
  cin >> t;

  while (t--) {
    int a, b;
    cin >> a >> b;
    if (b % a == 0) {
      cout << 0 << endl;
      continue;
    }

    bool found = false;
    int mi = 2e9;
    for (int k = 2; k * a < b; k++) {
      int num = b - k * a;
      int den = k - 1;
      int x = num / den;
      if (num % den == 0) {
        if ((b + x) % ((a + x) * k) == 0) {
          mi = min(mi, x);
          found = true;
        }
      }
    }



    if (found) {
      cout << mi << endl;
    } else {
      cout << -1 << endl;
    }
  }

  return 0;  
}