Answer
8.9 seconds
Work Step by Step
$h=-16t^2+20t+1100$
$0=-16t^2+20t+1100$
$x=(-b±\sqrt {b^2-4ac})/2a$
$x=(-20±\sqrt {20^2-4*-16*1100})/2*-16$
$x=(-20±\sqrt {400+6400*11})/-32$
$x=(-20±\sqrt {400+70400})/-32$
$x=(-20±\sqrt {70800})/-32$
$x=(-20±266.08)/-32$
We usually want the positive value of the square root since we are talking about time. However, since we have a negative denominator, we need the negative square root to get rid of the negative denominator.
$x=(-20±266.08)/-32$
$x=(-20-266.08)/-32$
$x=-286.08/-32$
$x=8.94$
