No problem, thank for helping!
It's from AOPS, but it never says the combined length of all different edges, it says the combined length of all its edges.
Oh well it turns out that "all of the edges" is every edge not every different one at least I think.
Thank you, but I'm a little confused... Which sides are a, b, and c? Why are there only 3 sides? Isn't it a rectangular prism?
+17 