#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch <= '9' && ch >= '0') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
const int maxn = 100 + 10;
const int mod = 1e6 + 7;
int main() {
  int t;
  cin >> t;
  while (t--) {
    long long n;
    int s;
    cin >> n >> s;
    string str = to_string(n);
    int len = str.length();
    int cnt = 0;
    for (int i = 0; i < len; i++) {
      cnt += str[i] - '0';
    }
    if (cnt <= s) {
      cout << 0 << endl;
      continue;
    }
    cnt = 0;
    if (str[0] - '0' >= s) {
      int mark = -1;
      for (int k = len - 1; k > 0; k--) {
        if (str[k] - '0' != 0) {
          mark = k;
          break;
        }
      }
      if (mark == -1) {
        cout << 10 - (str[0] - '0');
        for (int k = 1; k < len; k++) cout << 0;
        cout << endl;
        continue;
      } else {
        int first = 1;
        for (int k = 0; k < len; k++) {
          if (k < mark) {
            if (first && str[k] == '9')
              continue;
            else {
              cout << 9 - (str[k] - '0');
              first = 0;
            }
          } else if (k == mark)
            cout << 10 - (str[k] - '0');
          else if (k > mark)
            cout << 0;
        }
        cout << endl;
        continue;
      }
    } else {
      for (int i = 0; i < len; i++) {
        cnt += str[i] - '0';
        if (cnt >= s) {
          int mark = -1;
          for (int k = len - 1; k > i; k--) {
            if (str[k] != '0') {
              mark = k;
              break;
            }
          }
          if (mark == -1) {
            cout << 10 - (str[i] - '0');
            for (int k = i + 1; k < len; k++) cout << 0;
            cout << endl;
            break;
          } else {
            int first = 1;
            for (int k = i; k < len; k++) {
              if (k < mark) {
                if (first && str[k] == '9')
                  continue;
                else {
                  cout << 9 - (str[k] - '0');
                  first = 0;
                }
              } else if (k == mark)
                cout << 10 - (str[k] - '0');
              else if (k > mark)
                cout << 0;
            }
            cout << endl;
            break;
          }
        }
      }
    }
  }
  return 0;
}
