Frank was shoveling driveways for during the winter for some extra cash. He charged 12 dollars per driveway. After 19 driveways he had 280 dollars. How much money did
he start with?

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.