How does the Surface Area formula: 2B+L (2 times the bases plus the lateral surface area) applies to the finding the surface area of a right prism and right cylinder?

Aconstruction worker needs to put a rectangular window in the side of a building he knows from measuring that the top and bottom of the window have a width of 8bfeet and the sides have a length of 15 feet he also measured one diagonal to be 17 feet what is the length of the other diagonal