Sandy has four boxes filled with pink ribbons and yellow ribbons. the table shows the number of pink and yellow ribbons in each box. a fifth box has pink and yellow ribbons in the same proportion as sandy’s first four boxes. which tables could represent box number 5?

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.