A candy store at the mall sells Sugar Twists for $5.25 per pound and Pink Hearts for $6.00 per pound. If they sell four times as many pounds of Pink Hearts as Sugar Twists and take in $789.75, how many pounds of Pink Hearts did they sell? Do not enter units.

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.