The students at Camden Middle School went on a class ski trip. Each student paid $125 and the school paid a total of $300. Altogether, the trip cost at most
$2,425. How many students went on the trip?
PART A write an equation for this situation

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.