Please whoever knows they can solve this, help! I have attached the question down below. Please explain in detail and diagrams if the question permits you to do so. Thank you. I will also be marking the brainiest.

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.