5. How many rectangles are on am x n-size "chessboard"? For example, there are nine rectangles on a 2 x 2-size board: The whole board, 4 smaller squares and 4 ways in which 2 squares make a rectangle....

Extracted text: 5. How many rectangles are on am x n-size "chessboard"? For example, there are nine rectangles on a 2 x 2-size board: The whole board, 4 smaller squares and 4 ways in which 2 squares make a rectangle. Check your answer by calculating the number of rectangles on a 3 x 3-size chess board.