#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("avx2")
#pragma GCC optimization("unroll-loops")
using namespace std;
using ll = long long;
const int mod = (int)1000000007;
void solve() {
  ll n, s;
  cin >> n >> s;
  deque<int> num, res;
  ll dup = n;
  while (dup) {
    num.emplace_front(dup % 10);
    dup /= 10;
  }
  res.resize(num.size());
  int tot = 0, idx = -1;
  while (tot < s) tot += num[++idx];
  bool carry = false;
  bool first = true;
  if (accumulate(num.begin(), num.end(), 0) <= s) {
    cout << 0 << endl;
    return;
  }
  string second = to_string(n);
  string ss1;
  for (int i = 0; i <= idx; i++) ss1 += second[i];
  string ss2;
  for (int i = idx + 1; i < second.length(); i++) ss2 += '0';
  ll ans1 = stoll(ss1);
  while (ans1 % 10 != 0) ans1++;
  ans1 = stoll(to_string(ans1) + ss2);
  cout << ans1 - n << endl;
}
int main(int argc, char *argv[]) {
  clock_t clk_start = clock();
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  int cases = 1;
  cin >> cases;
  for (int i = 1; i <= cases; i++) {
    solve();
  }
  cerr << "Execution Time: " << fixed
       << double(clock() - clk_start) / double(CLOCKS_PER_SEC)
       << setprecision(6) << " sec\n";
}
