A shark can swim at an average speed of 25 miles per hour. At this rate, how far can a shark swim in 2.4 hours. Use r= d/t. (D over T)

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.