import math
t=int(input())
for _ in range(t):
  n,x=map(int,input().split())
  h=list(map(int,input().split()))
  v=list(map(int,input().split()))
  for i in range(n):
    if v[i]==0:
      v[i]=1000000000000000000000
    else:
      v[i]=1/v[i]
  x/=2
  ans=x/v[0]
  currmax=v[0]
  for i in range(1,n):
    currdist=0
    ans1=0
    fail=0
    if v[i]>currmax:
      currmax=v[i]
      currsin=v[0]/v[i]
      for j in range(i):
        theta=math.asin(currsin)
        currdist+=h[j]*math.tan(theta)
        if currdist>x:
          fail=1
          break
        ans1+=h[j]/(math.cos(theta)*v[j])
        currsin=currsin*v[j+1]/v[j]
      ans1+=(x-currdist)/v[i]
      if fail==0:
        ans=min(ans1,ans)
    print(2*ans)