#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
using namespace std;

int q, n;
double cost;
float var[4100][4100];
double ans[4100][4100];
int p[4100];
bool used[4100];
bool g[4100];

void precalc()
{
    var[0][0] = 1.;
    for (int i = 1; i < 4050; i++)
        var[i][0] = var[i - 1][0] * (double)i;
    for (int num = 2; num < 4050; num++)
    {
        var[num][1] = (double)(num - 1) * var[num - 1][0];
        for (int sngl = 2; sngl <= num; sngl++)
        {
            var[num][sngl] = (double)(sngl - 1) * var[num - 1][sngl - 2] + (double)(num - sngl) * var[num - 1][sngl - 1];
        }
    }
    ans[0][0] = 0.;
    for (int i = 1; i < 4050; i++)
        ans[i][0] = ans[i - 1][0] + 1. / (double)i;
    for (int i = 1; i < 4050; i++)
        ans[i][1] = ans[i - 1][0];
    for (int num = 2; num < 4050; num++)
    {
        for (int sngl = 2; sngl <= num; sngl++)
        {
            ans[num][sngl] = (double)(sngl - 1) * var[num - 1][sngl - 2] / var[num][sngl] * ans[num - 1][sngl - 2] + (double)(num - sngl) * var[num - 1][sngl - 1] / var[num][sngl] * ans[num - 1][sngl - 1];
//          var[num][sngl] = (double)(sngl - 1) * var[num - 1][sngl - 2] + (double)(num - sngl) * var[num - 1][sngl - 1];
        }
    }
    return;
}

int main()
{
//  freopen("input.txt", "r", stdin);
//  freopen("output.txt", "w", stdout);

    precalc();

    scanf("%d", &q);
    while(q--)
    {
        cin >> n >> cost;
        for (int i = 0; i < n; i++)
            used[i] = g[i] = 0;
        for (int i = 0; i < n; i++)
        {
            cin >> p[i];
            p[i]--;
            if (p[i] != -1)
                g[p[i]] = 1;
        }
        int cycles = 0, sngl = 0, num = 0;
        for (int i = 0; i < n; i++)
        {
            if (g[i])
                continue;
            num++;
            if (p[i] == -1)
                sngl++;
        }
        cycles = -num;
        for (int i = 0; i < n; i++)
        {
            if (used[i])
                continue;
            cycles++;
            int v = i;
            while (v != -1 && !used[v])
            {
                used[v] = 1;
                v = p[v];
            }
        }
        double a = (double)cycles + ans[num][sngl];
        printf("%.10lf\n", a * cost);
    }

    return 0;
}