5x13 is 65...you have 65 becuase both triangles are there... 5x16 is 80... so 145... 13x16 is 208, so 353 so far. 7x16 is 112, so 465 so far. ANother 112 for the other side is 577. 12x7 is 84 times two for both sides, which is 168. 577+168 is 745. I believe that is your final area of the surface area, 745 Square feet.