from copy import deepcopy

def arGeoSeq(a1,d1,k1,r1):
    return (a1-d1*k1)*r1**(k1-1)

def arGeoSeqDer(a1,d1,k1,r1):
    if(k1 == 1):
      return 0
    else:
      return (k1-1)*(a1-d1*k1)*r1**(k1-2)
        
def arGeoSer(a2,d2,n2,r2):
    res = 0
    for i in range(1,n2+1):
        res += arGeoSeq(a2,d2,i,r2)
    return res

def arGeoSerDer(a2,d2,n2,r2):
    res = 0
    for i in range(1,n2+1):
        res += arGeoSeqDer(a2,d2,i,r2)
    return res
    
q = int(input())
for i in range(q):
    temp = input().split(' ')
    a, d, n, x = int(temp[0]), int(temp[1]), int(temp[2]),int(temp[3])
    r = 1
    counter = 0
    while(True):
        temp = deepcopy(r)
        fx = arGeoSer(a,d,n,r) + x
        fxDer = arGeoSerDer(a,d,n,r) + x
        # print(counter,r,fx,fxDer)
        r = r - fx/fxDer
        if(r == temp):
            break
        counter += 1
    print(r)