Identify the dependent and independent variables. The amount of items in a carton depends on the size of the carton.
The dependent variable is the the size of the carton or amount of item
The independent variable is the size of the carton or amount of item

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.