#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long int t;
  cin >> t;
  while (t--) {
    string str;
    long long int x;
    cin >> str >> x;
    long long int n = str.length(), sum = 0, idx, flag = true;
    for (long long int i = 0; i < n; i++) {
      sum += str[i] - '0';
      if (sum >= x and flag) idx = i, flag = false;
    }
    if (sum <= x)
      cout << 0;
    else {
      long long int y = 0, z = 1;
      for (long long int j = idx; j < n; j++)
        y = y * 10 + (str[j] - '0'), z *= 10;
      cout << z - y;
    }
    cout << "\n";
  }
  return 0;
}
