What are the equations?

I assume you want to know a permutation about how many ways they can be in the final set-up.

Order matters, which is why this is a permutation.

Formula: P(n, r) = 

where the permutation is , with P for permutation.

Plug in:

4!/(4-2)!
4!/2!
(1 x 2 x 3 x 4)/1 x 2
(3x4)/1
= 12

12 ways.