#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int a, b;
    cin >> a >> b;
    if (a % b == 0) {
      cout << 0 << endl;
      continue;
    }
    int ans = (((a / b) + 1) * b) - a;
    cout << ans << endl;
  }
  return 0;
}
