#nullable enable

#region
var (_input, _iter) = (Array.Empty<string>(), 0);
T I<T>() where T : IParsable<T>
{
    while (_iter >= _input.Length) (_input, _iter) = (Console.ReadLine()!.Split(' '), 0);
    return T.Parse(_input[_iter++], null);
}
#endregion

static T[] Range<T>(int n, Func<T> F) => Enumerable.Range(0, n).Select(_ => F()).ToArray();

long Solve()
{
    var n = I<int>();
    var k = I<int>();
    var az = Range(n, I<int>);
    Array.Sort(az);
    long ans = az[0] - k;
    if (ans <= 0) return 0;
    for (var i = 1; i < n; i++) ans *= az[i];
    return ans;
}
var t = I<int>();
var ans = Range(t, Solve);
Console.WriteLine(string.Join(Environment.NewLine, ans));