Factor polynomials into irreducibles over GF(q)

Question

The polynomials $x^4+x^3+1$ and $x^4+x^3+x^2+x+1$ are irreducibles over GF(2).

(a) Factor both polynomials into irreducibles over GF(4). (b) Factor both polynomials into irreducibles over GF(8).

I simply don't have a clue how to do that. Can someone please give me a hand?

Thanks in advance.