#include <bits/stdc++.h>
using namespace std;
template <typename T>
inline T READ() {
  T X = 0;
  bool flag = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') flag = 0;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    X = (X << 1) + (X << 3) + ch - '0';
    ch = getchar();
  }
  if (flag) return X;
  return ~(X - 1);
}
int re(long long n) {
  int sum = 0;
  while (n) {
    sum += n % 10;
    n /= 10;
  }
  return sum;
}
int main() {
  int T = READ<int>();
  while (T--) {
    long long n = READ<long long>();
    int s = READ<int>();
    long long u = n;
    int now = re(n);
    long long pow2 = 10;
    while (now > s) {
      n /= pow2;
      n++;
      n *= pow2;
      pow2 *= 10;
      now = re(n);
    }
    cout << n - u << endl;
  }
}
