The following table shows the number of lemons that grew on Mary’s lemon tree each season last year. Number of lemons. Winter 3. Spring 15 summer 21 fall 13 find the mean number of lemons

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.