The following gure consists of 8 horizontal lines and 15 vertical lines. The goal of this problem is to count the number of rectangles (squares are a kind of rectangle, but line segments are not). Let V be the set of all sets of two vertical lines, and let H be the set of all sets of two horizontal lines. Let R be the set of all rectangles in the gure. Dene a function f: R a V K H by A C :l L ({AB, CD}, {AC, BD}). 3 D Compute IRI, the number of rectangles in the gure