2x^2 ? (2x)^2 ?.....?

Question

im stuck on that part on this question:

c^12 - 27d^6

using formula

a^3 - b^3 = (a + b) (a^2 - ab + b^2)

on the last b^2 part of the formula, is it 9d^4 or 3d^4?

Answer 1

it should be 9d^4