#include <bits/stdc++.h>
using namespace std;
vector<int> fr;
int main() {
  int t;
  cin >> t;
  while (t--) {
    long long int n, m;
    cin >> n >> m;
    string s = to_string(n);
    double sum = 0;
    for (int i = 0; i < s.length(); i++) {
      sum += s[i] - '0';
    }
    if (sum <= m) {
      cout << "0\n";
    } else {
      int idx = -1;
      int temp = 0;
      for (int i = 0; i < s.length(); i++) {
        temp += s[i] - '0';
        if (temp < m) {
          idx = i;
        } else
          break;
      }
      unsigned long long int val = 0, val1 = 1;
      for (int i = idx + 1; i < s.length(); i++) {
        val = val * 10 + s[i] - '0';
        val1 = val1 * 10;
      }
      unsigned long long int ans = val1 - val;
      cout << ans << "\n";
    }
  }
  return 0;
}
