#include <iostream>
#include <algorithm>
#include <vector>
#include <cmath>
#include <iomanip>
#define INF 2140000000
using namespace std;

void solve()
{
    int n, x;
    cin >> n >> x;
    vector<int> h(n), a(n);
    int i, j;
    int preh = 0;
    for (i = 0; i < n; i++) {
        int curh; cin >> curh; 
        h[i] = curh - preh; preh = curh;
    }
    for (i = 0; i < n; i++) {
        cin >> a[i];
    }
    double ans = (double)x * a[0];
    int mina = INF;
    for (i = 0; i < n; i++) {
        if (a[i] < mina) {
            double sumdist = 0;
            double sumtime = 0;
            for (j = 0; j < i; j++) {
                double sint = (double)a[i] / a[j];
                double cost = sqrt(1 - sint * sint);
                double dist = sint/cost * h[j];
                sumdist += dist;
                sumtime += (double)h[j] / cost * a[j] * 2;
            }
            if (sumdist * 2 < x) {
                ans = min(ans, sumtime + (x - sumdist * 2) * a[i]);
            }
        }
        mina = min(mina, a[i]);
    }
    cout << setprecision(10) << ans << endl;
    return;
}

int main()
{
    int T, t;
    cin >> T;
    for (t = 0; t < T; t++) {
        solve();
    }
    return 0;
}