A radio station is giving away tickets to a play. They plan to give away tickets for
seats that cost $10 and $20. They want to give away at least 20 tickets. The total
cost of all the tickets they give away can be no more than $280. Let x = number
of $10 tickets and y = number of $20 tickets, which inequality system is correctly
set up to solve this problem?

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.