sequences and series - How can I evaluate $sum_{n=1}^{infty} n^{3}x^{n-1}$

How do i evaluate :

$$\sum_{n=1}^{\infty} n^{3}x^{n-1}$$

The answer is supposed to be: (according to wolfram alpha)

$$ \frac{x^2+4x+1}{(x-1)^4} $$

I have only learned to to this for simpler geometric sums.