# The height in feet of a golf ball hit into the air is given by h= -16t^2 + 64t, where t is the number of seconds elapsed since the ball was hit. How long does it take for the ball to reach the maximum height?

$h = - 16 {t}^{2} + 64 t$.
$t = - \frac{b}{2 a} = - \frac{64}{-} 32 = 2$ sec.