What is dy/dx when y=(x^2 - 4x ) ^3 ?

A. 3(x^2 -4x)^2
B. (6x - 12) (x^2 -4x)^2
C. 3(2x - 4)^2
D. 6x^2(2x-4)^2

first line derivative:

dy/dx = 3(x^2 -4x)^2 (2x-4)
= 3(x^2)(x-4)^2 (2)(x-2)
= 6x^2 (x-2)(x-4)^2

B is the correct choice, but it is not fully simplified