#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops, no-stack-protector")
#pragma GCC target("avx,avx2,fma")
using namespace std;
long long int digit_sum(long long int n) {
  long long int sum = 0;
  while (n > 0) {
    sum += n % 10;
    n /= 10;
  }
  return sum;
}
int main() {
  ios::sync_with_stdio(false), cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int s;
    long long int n;
    cin >> n >> s;
    long long int sum = digit_sum(n);
    long long int divider = 10;
    long long int cost = 0;
    while (sum > s) {
      long long int value = n % divider;
      if (value == 0) {
        divider *= 10;
        continue;
      }
      cost += divider - value;
      n += divider - value;
      sum = digit_sum(n);
      if (divider != 1000000000000000000) {
        divider *= 10;
      }
    }
    cout << cost << endl;
  }
}
