A ball is thrown at a velocity of 16ft/sec off the top of a roof 320 feet above the ground.
a) Use the formula s=-16t^2 + v0t +s0 to write the equations which describes the height of the ball above the ground, s, in t seconds after the fall begins.
s=-16t^2 + 16t +320
b) How long will it take the ball to hit the ground?
How do I figure out the answer for part b?