Answer:
The height as a function of time is
h(t) = -(1/2)gt2 + v0t + h0
h(t) = -16t2 + 32t + 20
The ball reaches the ground when h(t) = 0
-16t2 + 32t + 20 = 0
Solve this quadratic equation for t. You will get a positive solution and a negative solution. Discard the negative solution, since time begins at t=0 at the moment the ball is struck. Can you finish from here?