#include <bits/stdc++.h>
using namespace std;
long long chartoint(char *ch, long long n) {
  long long res = 0;
  for (long long i = 0; i < n; i++) {
    res = res * 10 + ch[i] - '0';
  }
  return res;
}
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  long long t;
  cin >> t;
  while (t--) {
    long long n = 0;
    char a[20], b[20];
    long long s;
    cin >> a >> s;
    for (long long i = 0; a[i] != '\0'; i++) b[i] = a[i], n++;
    long long res = 0, ptr = 0;
    while (res < s && ptr < n) res += a[ptr++] - '0';
    bool zero = true;
    for (long long i = ptr; i < n; i++)
      if (a[i] != '0') zero = false;
    if (res < s || (res == s && zero)) {
      cout << 0 << endl;
    } else {
      ptr--;
      ptr--;
      long long tail = ptr;
      while (ptr >= 0) {
        if (b[ptr] - '0' + 1 == 10) {
          b[ptr] = '0';
          ptr--;
        } else {
          b[ptr]++;
          break;
        }
      }
      for (long long i = max(0ll, tail + 1); i < n; i++) b[i] = '0';
      if (ptr < 0) {
        long long tmp = 1;
        for (long long i = 0; i < n; i++) tmp = tmp * 10;
        cout << tmp - chartoint(a, n) << endl;
      } else {
        cout << chartoint(b, n) - chartoint(a, n) << endl;
      }
    }
  }
  return 0;
}
