Answer
6.5 seconds
Work Step by Step
$h=-16t^2+20t+1100$
$550=-16t^2+20t+1100$
$0=-16t^2+20t+550$
$0/-2=(-16t^2+20t+550)/-2$
$0=8t^2-10t-275$
$x=(-b±\sqrt{b^2-4ac})/2a$
$x=(-(-10)±\sqrt{(-10)^2-4*8*-275})/2*8$
$x=(10±\sqrt{100+32*275})/16$
$x=(10±\sqrt{100+8800})/16$
$x=(10±\sqrt{8900})/16$
$x=(10±94.34)/16$
We want only the positive value for $x$ since we are talking about time.
$x=(10±94.34)/16$
$x=(10+94.34)/16$
$x=104.34/16$
$x=6.52$
