Units in a quotient of a polynomial ring
How can I do calculations in a quotient ring using sage? For example, I would like to find all the units (or at least count the number of units) in this quotient ring. Z_4[x]/(x^4+1, 2+2x). (Here Z_4 is the ring of integers mod 4.) Is that possible? I could not find any useful documentation for quotients of polynomial rings that are not a PID. Any help would be greatly appreciated. Thank you.