A ball is hit with an intial speed of \( 900 \) feet per second. The height s of the ball (in feet) as a function of time (in seconds) can be modeled by the function \( s ( t ) = - 16 t ^ { 2 } + 300 t \) .
(a) When will the height of the ball be \( 900 \) teet?
(b) When will the ball hit the ground?