Finding a proof for a composite number statement

Question

I've been trying to solve this specific proof problem, but I don't seem to be able to figure out how to start with the proof.

Here it is:

For all $a\in\mathbb Z_+$ with $a > 3$ , $a^2 - 4$ is composite

Answer 1

Since $a>3$ we get that $a-2>1$. Now, $a^2-4=(a+2)(a-2)$ and both the factors are greater than $1$, hence it is a composite number.