#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for (int i = a; i < b; i++)
using ll = long long;

int main(){
	int t;
	cin >> t;
	rep(ti, 0, t) {
		int n, k;
		cin >> n >> k;
		vector<int> a(n);
		rep(i, 0, n) cin>> a[i];
		ll ans = 1e18, b = 1;;
		rep(i, 0, n) b *= a[i];
		rep(i, 0, n) {
			ll c = b / a[i];
			c *= a[i] - k;
			ans = min(ans, c);
		}
		cout << ans << endl;
	}
}