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