#include <stdio.h>
#include <math.h>

const long double eps = 1e-9;

void chmin(long double *a, long double b)
{
	if (*a > b) *a = b;
}

long double solve()
{
	int i, N, H[101], A[101];
	long double X;
	scanf("%d %Lf", &N, &X);
	for (i = 1, H[0] = 0; i <= N; i++) scanf("%d", &(H[i]));
	for (i = 1; i <= N; i++) scanf("%d", &(A[i]));
	
	int j, k;
	long double ans = X * A[1], tmp, Y, Z;
	for (k = 2; k <= N; k++) {
		for (j = 1; j < k; j++) if (A[j] <= A[k]) break;
		if (j < k) continue;
		
		for (j = 1, Y = X, tmp = 0; j < k; j++) {
			Z = sqrtl((long double)A[k] * A[k] / ((long double)A[j] * A[j] - (long double)A[k] * A[k]));
			Y -= Z * (H[j] - H[j-1]) * 2.0;
			if (Y < -eps) break;
			tmp += sqrtl(1.0 + Z * Z) * (H[j] - H[j-1]) * 2.0 * A[j];
		}
		if (j == k) chmin(&ans, tmp + Y * A[k]);
	}
	return ans;
}

int main()
{
	int T;
	scanf("%d", &T);
	while (T--) printf("%.9Lf\n", solve());
	fflush(stdout);
	return 0;
}