A fisherman Can row upstream at 1mph and downstream 4 mph. He started rowing upstream until he got tired and then towed downstream to his starting point. How far did the fisherman row if the entire trip took 6 hours?

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.