An ant in a room where the length is 20 ft width is 15 ft an

An ant in a room where the length is 20 ft, width is 15 ft and height is 10 ft. The ant is located at one corner of the cube (call it point A), that wants to crawl to the opposite corner of the cube (call it point B). Find the length of the shortest path the ant can take from point A to point B. Note that the ant cannot fly: it must crawl along the walls (i.e., along the surface of the cube). This question can be answered using calculus or without calculus, both is fine but I would rather know the calculus method.