Answer
$2$ seconds
Work Step by Step
To find out how long it takes the diver to reach the pool, we want to know the value of $t$ for which $h=0$:
$$0=-16t^2+64$$
Factor out $-16$:
$$0=-16(t^2-4)$$
$$t^2-4=0$$
$$t^2=4$$
Get the squareroot of both sides:
$$\sqrt{t^2}=4$$
$$t=±2$$
Since the time $t$ cannot be negative, the proposed solution is $2$ seconds.
