I've been stumped on this problem for a while now, unable to find many resources to help me understand how to describe a preimage of a set given a function like this one. 

Let $f$: $\mathbb Z \to \mathbb Z$ be the function defined by *f(n)* = the last digit of *n*. For example, $f(-234)=4$

Describe the premiere of the set {0, 2, 4, 6, 8}