Introduction to Discrete Mathematics

Hey I'm in my first term for Discrete Mathematics and still fairly confused with most of it. Anyway I came into some trouble on my homework, and I don't necessarily need anyone to solve it for me but kind of give me a push in right direction with some examples or explanations, because I really need to get it done and can't get hold of my instructor that quickly. I have an idea as to what I need to do, but can't really bring it all together right now so I'm really hoping someone can help me a little more than my book.

Let A = {1, 2, 3, 4} and B = {x ∈ ℤ | x mod 2 = 0}. Let R: A → B be a relation such that (x, y) ∈ R → x/y ∈ ℤ.

a) Write R in set roster notation.

b) Draw an arrow diagram for R.

c) Show why R is or is not a function.