from math import sqrt
T = int(input())
for _ in range(T):
    N, X = map(int, input().split())
    H = [int(a) for a in input().split()]
    A = [int(a) for a in input().split()]
    HH = [H[0]] + [h2 - h1 for h1, h2 in zip(H, H[1:])]
    mi = ans = 1 << 60
    for i in range(N):
        if A[i] >= mi: continue
        mi = A[i]
        t = 0
        sx = 0
        for j in range(i):
            a = A[i] / A[j]
            b = sqrt(1 - a ** 2)
            t += A[j] * HH[j] / b
            sx += a * HH[j] / b
        if sx * 2 > X: continue
        t += (X / 2 - sx) * A[i]
        if t * 2 < ans:
            ans = t * 2
    print(ans)