evaluate the limit using change of variable

Question

x--> 27
27-x
_________
x^1/3 -3
(answer is 1/12)

Answer 1

derivative of top = -1
derivative of bottom = (1/3) x^-(2/3)

ratio = -3/27^(2/3)
= -3 /3^2 = -3/9 = -1/3