Asap nina is participating in a swim-a-thon to raise money for a charity. for every lap that nina swims, her grandmother has promised to donate $2.50. if nina swims 18 laps, how much will her grandmother donate? a.$45.00 b.$20.50 c.$18.00 d.$7.20

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.