#include <bits/stdc++.h>
using namespace std;
const double eps = 0.0000000001;
const double PI = acos(-1);
int main(){
  cout << fixed << setprecision(20);
  int T;
  cin >> T;
  for (int i = 0; i < T; i++){
    int N, X;
    cin >> N >> X;
    vector<int> H(N + 1);
    H[0] = 0;
    for (int j = 1; j <= N; j++){
      cin >> H[j];
    }
    vector<int> A(N);
    for (int j = 0; j < N; j++){
      cin >> A[j];
    }
    double ans = (long long) X * A[0];
    for (int j = 1; j < N; j++){
      vector<double> t(j + 1);
      t[j] = PI / 2;
      bool ok = true;
      for (int k = j - 1; k >= 0; k--){
        double s = sin(t[k + 1]) * A[k + 1] / A[k];
        if (s > 1 - eps){
          ok = false;
          break;
        }
        t[k] = asin(s);
      }
      if (ok){
        double x = 0, time = 0;
        for (int k = 0; k < j; k++){
          x += (H[k + 1] - H[k]) * tan(t[k]);
          time += (H[k + 1] - H[k]) / cos(t[k]) * A[k];
        }
        if (x <= X / 2){
          time *= 2;
          time += A[j] * (X - x * 2);
          ans = min(ans, time);
        }
      }
    }
    cout << ans << endl;
  }
}