#include <bits/stdc++.h>

using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned;
using u128 = unsigned __int128;

void solve() {
    int N, V;
    std::cin >> N >> V;
    
    double ans = 0;
    for (int i = 0; i < N; i++) {
        int x;
        std::cin >> x;
        ans += std::sqrt(x);
    }
    ans *= ans;
    ans /= V;
    std::cout << ans << "\n";
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    std::cout << std::fixed << std::setprecision(10);
    
    int t;
    std::cin >> t;
    
    for (int i = 1; i <= t; i++) {
        std::cout << "Case " << i << ": ";
        solve();
    }
    
    return 0;
}