Answer
When $$t=11sec$$
Work Step by Step
We have $$h(t) = -16t^2+96t+880 = -16(t-11)(t+5)$$
When hit the ground the position will be $0ft$, so $$-16(t-11)(t+5) = 0$$
Solving the parenthesis 1)$$t-11=0$$ $$t=11$$
2)$$t+5=0$$ $$t=-5$$
As time can not be negative then $$t=11sec$$
