Scientists working on a new rocket conduct a test launch with an initial velocity of 300 m/sec from a height of 500 m. Its height, (h), in meters, after (t) seconds is given by the formula h = 500+
3001 - 9.812. After how many seconds will the rocket reach a height of O m?

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.