I am asked to solve the following recurrence relations...that is find a closed form for them. I am supposed to do this using "back substitution"

a) a sub n = 4a sub n-1 + 5 for all n > 0 and a sub 0 = 2.

b) b sub n = b sub n-1 + n^2 for all n > 0 and b sub 0 = 3.

Any suggestions?? Thank you.