Untitled

#include<bits/stdc++.h>
#define ll long long
#define endl "\n"
using namespace std;
template<class T>
void printff(vector<T>& v) {
  for (auto k : v) cout << k << " ";
  cout << endl;
}
int n;
ll k;
ll target;
bool check(vector<ll> & a, ll mid){
    ll sum = 0;
    for(int i = 0; i < n; i++){
        sum += (a[i] / mid);
        if (sum >= target) return true;
    }
    return false;
}
void SOLVE() {
  cin >> n >> k;
  target = k * k;
  vector<ll> a(n);
  for(auto & val : a) cin >> val;

  ll l = 0, r = 1e10 + 1;
  while(r - l > 1){
    ll mid = (l + r) >> 1LL;
    if(check(a, mid)) l = mid;
    else r = mid;
  }
  if(l == 0) cout << -1 << endl;
  else cout << l << endl;
}
int main() {
  ios_base::sync_with_stdio(false); 
  cin.tie(NULL); 
  cout.tie(NULL);
  int tc = 1; cin >> tc;
  while(tc--) SOLVE();
  return 0;
}