Arectangular piece of poster board measures 60 centimeters by 80 centimeters. linn draws the net of a box on the poster board and cuts it out. if the box measures 10 centimeters by 16 centimeters by 27 centimeters, what is the area of the poster board left?

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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.