import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
md = 10**9+7
# md = 998244353
input = sys.stdin.readline

from decimal import Decimal

def solve():
    n, x = LI()
    hh = [Decimal(0)]+list(map(Decimal, input().split()))
    aa = list(map(Decimal, input().split()))

    ans = inf
    mn = inf
    for i, a in enumerate(aa):
        if a >= mn: continue
        mn = a
        di = Decimal(x)
        t = Decimal(0)
        for j in range(i):
            h = hh[j+1]-hh[j]
            d = a*h/(aa[j]**2-a**2).sqrt()
            di -= d*2
            t += (d**2+h**2).sqrt()*aa[j]*2
        if di < 0: break
        t += di*a
        ans = min(ans, t)

    print(ans)

for _ in range(II()):
    solve()