{0}xZ2 is the kernel of pi because pi(0xz2)=0 for any z2 in Z2. It can be shown that pi: Z4xZ2→Z4 is a homomorphism, therefore the canonical map Pi: Z4xZ2/{0}xZ2→Z4 is isomorphism, so Z4xZ2/{0}xZ2 and Z4 are isomorphic. I don't see why you need the theorem about finite abelian group, maybe this is just an example of that theorem.