In Integral Domain, D, every associate of an irreducible [resp. prime] element of D is irreducible [resp. prime].
I am done with irreducible part.
For prime, I am stuch with this idea. So if p is prime, let say x is an associate of p then p=xd for some d in D. Since p is prime, then p|x or p|d. We need to show that d is prime. How?