// @author godmar
import java.util.*;
import java.util.function.*;
import java.io.*;
import static java.lang.Math.*;

public class godmar {
    public static void main(String ...av) {
        var sc = new Fast.Scanner();
        var T = sc.nextInt();
        PrintWriter pw = new PrintWriter(System.out);
        for (int i = 0; i < T; i++)
            pw.println(doOne(sc));
        pw.close();
    }

    static double doOne(Fast.Scanner sc) {
        int n = sc.nextInt();
        long p = sc.nextLong();
        double D = 0;
        long [] ti = new long[n];
        for (int i = 0; i < n; i++) {
            ti[i] = sc.nextLong();
            D += ti[i];
        }
        double λ = p/D;     // compute Lagrange multiplier in O(1)
        double s = 0;
        for (int i = 0; i < n; i++)
            s += ti[i] * λ * λ;

        return s;
    }
}

class Fast
{
    //-----------Scanner class for faster input----------
    /* Provides similar API as java.util.Scanner but does not
     * use regular expression engine.  
     */
    public static class Scanner {
        BufferedReader br;
        StringTokenizer st;

        public Scanner(Reader in) {
            br = new BufferedReader(in);
        }

        public Scanner() { this(new InputStreamReader(System.in)); }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() { return Integer.parseInt(next()); }
        long nextLong() { return Long.parseLong(next()); }
        double nextDouble() { return Double.parseDouble(next()); }

        // Slightly different from java.util.Scanner.nextLine(),
        // which returns any remaining characters in current line,
        // if any.  
        String readNextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
        int[] readIntArray(int n) {
            int[] a = new int[n];
            for (int idx = 0; idx < n; idx++) {
                a[idx] = nextInt();
            }
            return a;
        }
        long[] readLongArray(int n) {
            long[] a = new long[n];
            for (int idx = 0; idx < n; idx++) {
                a[idx] = nextLong();
            }
            return a;
        } 
    }
    //--------------------------------------------------------    
}