A large rectangle is divided into 4 non-overlapping smaller rectangles by two lines. One line is parallel to the base, and the other line is parallel to the height. If the areas of three of the small rectangles are 18,24, and 40, compute the only possible integer solution for the area of the fourth small rectangle. I'm not entirely sure where to start.

See:

http://www.jiskha.com/display.cgi?id=1306200821