find the coefficient of x^3 in the expansion of (1-3x)^-4

Question

I need the steps on how to find this answer, please

Answer 1

(1 - 3x)^-4

Use the binomial expansion to expand as follows till you get to the term with x^3.

⇒ term with x^3 = 20(27x^3)

                             = 540x^3

hence the coefficient is 540