The memory in Mary's phone allows her to take up to 20 pictures. Mary has already taken 16 pictures. Write an inequality to show how many more picture Mary could take

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.