#include <bits/stdc++.h>
using namespace std;
inline long long POW(long long n, long long m) {
  long long ans = 1;
  for (long long i = 1; i <= m; i++) {
    ans *= n;
  }
  return ans;
}
int main() {
  long long t;
  cin >> t;
  while (t--) {
    long long m;
    string s;
    cin >> s >> m;
    long long k = 0;
    long long sum = 0, sum1 = 0;
    for (long long i = 0; i < s.length(); i++) {
      sum1 = sum1 + s[i] - '0';
    }
    for (long long i = 0; i < s.length(); i++) {
      sum = sum + s[i] - '0';
      if (sum >= m) {
        k = i;
        break;
      }
    }
    if (sum1 <= m) {
      cout << "0" << endl;
      continue;
    }
    if (s.length() == 1) {
      cout << 10 - (s[0] - '0') << endl;
      ;
    } else {
      string w = "";
      for (int i = k; i < s.length(); i++) {
        w = w + s[i];
      }
      long long q = stoll(w);
      long long x;
      x = 1 * POW(10, s.length() - k) - q;
      cout << x << endl;
    }
  }
  return 0;
}
