#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int T, tt;
  cin >> T;
  for (tt = 0; tt <= T - 1; tt++) {
    int s, i = 0, sum = 0, no_digits = 0;
    int j;
    long long int n, tmp;
    cin >> n >> s;
    tmp = n;
    int a[18];
    while (tmp != 0) {
      a[i] = tmp % 10;
      i++;
      tmp = tmp / 10;
    }
    no_digits = i;
    for (i = no_digits - 1; i >= 0; i--) {
      sum += a[i];
    }
    if (sum <= s) {
      cout << "0" << endl;
    } else {
      int p = 0;
      for (i = no_digits - 1; i >= 0; i--) {
        p += a[i];
        if (p >= s) {
          break;
        }
      }
      long long int num = 0, jmp = 1;
      for (j = 0; j <= i; j++) {
        num += (jmp)*a[j];
        jmp *= 10;
      }
      cout << jmp - num << endl;
    }
  }
  return 0;
}
