#include <bits/stdc++.h>
using namespace std;
const long long maxn = 2e5 + 5;
int main() {
  long long t;
  cin >> t;
  while (t--) {
    string s1;
    long long n;
    cin >> s1 >> n;
    int sum = 0;
    long long ans = 0;
    int len = s1.size();
    for (int i = 0; i < len; i++) {
      sum += s1[i] - '0';
      if (n > sum) {
        n = n;
      } else if (n == sum) {
        int f = 0;
        for (int j = i + 1; j < len; j++) {
          if (s1[j] != '0') f = 1;
        }
        if (f == 0)
          break;
        else {
          ans = ans * 10 + s1[i] - '0';
          n--;
        }
      } else {
        ans = ans * 10 + s1[i] - '0';
      }
    }
    long long k = ans;
    long long xx = 1;
    int g = 0;
    if (k == 0) xx = 0;
    while (k) {
      g++;
      k = k / 10;
    }
    for (int i = 0; i < g; i++) xx = xx * 10;
    cout << xx - ans << "\n";
  }
  return 0;
}
