notice the picture below
the prism itself, is just 2 triangles and 3 rectangles, stacked up to each other at the edges
so, to get the surface area of it, just get the surface area of each of those triangles and rectangles, and sum them up
notice for the triangle, A = 1/2 bh, we have the base and the hypotenuse, to get the height, simply using the pythagorean theorem, we get what you see in the picture
