Mum is 25 years older than her son Max, but she is 1 year younger than dad. Sara is half as old as her brother Max.
The total age of the mum, dad and Max is 87 years.
How old is Sara?

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.