You also need to use product rule.

The two functions here are,

x^3

(2x-4)^4

The respective derivatives are:

3x^2----> Power rule

2*4(2x-4)^3=8(2x-4)^3---->Chain Rule

Now apply the product rule,

u'v+uv'

We have,

[3x^2][(2x-4)^4]+[x^3][8(2x-4)^3]

Thus,

3x^2(2x-4)^4+8x^3(2x-4)^3

Factor,

x^2(2x-4)^3[3(2x-4)+8x(2x-4)]

Open,

x^2(2x-4)^3[6x-4+16x^2-32x]

Thus,

x^2(2x-4)^3[16x^2-26x-4]

Factor,

2x^2(2x-4)^3(8x^2-13x-2)