Find all solutions of the recurrence relation $\displaystyle r_n = 4r_{n-1} +2^n$

I know how to do the linear ones but if someone could point me in the right direction to complete this one, that would be great. Thanks!

EDIT: I know the answer is $\displaystyle r_n = \alpha 4^n +2^{n+1}$ I just don't know how to get there.