A ball is thrown straight up from a rooftop 320 feet high. The formula below describes the​ ball's height above the​ ground, h, in​ feet, t seconds after it was thrown. The ball misses the rooftop on its way down and eventually strikes the ground. How long will it take for the ball to hit the​ ground? Use this information to provide tick marks with appropriate numbers along the horizontal axis in the figure shown.
h=-16t^2+16t+320
The ball hits the ground after____ seconds