physics
posted by Anonymous .
a rocket is launched from atop a 105foot cliff with an initial velocity of 156 ft/s.The height of the rocket above the ground at time or t is given by h=16tsquared+156t+105. When will the rocket hit the ground after it is launched?

when is h= 0?
0=h(t)=16t^2 + 156t+105
solve for t.