IF your equation is this: h(t)= -16t^2 + 27t + 7, then you set it equal to 17 and solve for t. What this does is tells you the times (t) when the ball is exactly 17 feet off the ground. Because this is a parabola, the ball will go up past the 17 foot mark, then pass it again on the way back down. This happens at .55 seconds (going up), and 1.13 seconds (coming down).
