Juli is going to launch a model rocket in her backyard. When she launches the rocket, the function h(t)=−16t2+32t models the height, h, of the rocket above the ground as a function of time, t. Find the zero of this function that tells us when the rocket will hit the ground after it is launched.

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.