#include <bits/stdc++.h>
using namespace std;
inline long long sum_of_digits(long long n) {
  long long sum = 0;
  while (n > 0) sum += n % 10, n /= 10;
  return sum;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int tests;
  cin >> tests;
  while (tests--) {
    long long N, S;
    cin >> N >> S;
    long long M = N;
    long long denom = 10;
    while (sum_of_digits(M) > S) {
      M = (M / denom + 1);
      if (M % 10 == 0) {
        denom *= 10;
        M /= 10;
      }
      M *= denom;
    }
    cout << M - N << "\n";
  }
  return 0;
}
