Answer
8.9 s
Work Step by Step
We know:
$$ 0 = -16t^2+20t+1100$$
We use the quadratic formula:
$$x= \frac{-b \pm \sqrt{b^2-4ac}}{2a}$$
$$x= \frac{16 \pm \sqrt{(-16)^2-4(-16)(1100)}}{2(-16)}$$
Since time must be positive, we only consider the positive answer:
t= 8.9s
