Corey has 42 feet of fencing around his garden. the garden is rectangular in shape, and its length is equal to twice the width minus 3 feet. define the variables, and write a system of equations to find the length and width of the garden

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.