John wants to magnify the image of a fire ant and a crab spider so they appear to be the same length. how many times their actual sizes would he need to magnify each image? the fire ant is 4 millimeters, crab spider is 5 millimeters.

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.