#include <iostream>
#include <vector>
#include <set>
#include <random>
#include <iomanip>

void doCase()
{
	int64_t n, p;
	std::cin >> n >> p;
	double tsum = 0;
	for (int i = 0; i < n; i++)
	{
		double t;
		std::cin >> t;
		tsum += t;
	}
	std::cout << std::setprecision(30) << double(p) * double(p) / tsum << std::endl;
}

int main()
{
	int T;
	std::cin >> T;
	for (int i = 0; i < T; i++)
		doCase();
}