The height h(in ft) above the ground of a submarine-launches missile is given by the function h=-16t+96t+80 where t represents the time in seconds. Scetch a graph of this function. Determine the time at which the missile leaves and returns to the water.
Your equation is not correct
First of all it should say
h = -16t^2 + 96t + ....
secondly the +80 at the end makes no sense.
Since it is launched from a submarine, then it would be launched 80 ft above sea level.
Don't know about that !! , sounds strange
let's assume the equation is as it stands,
let
-16t^2 + 96t + 80 = 0
t^2 - 6t - 5 = 0
t^2 - 6t + 9 = 5+9
(t-3)^2 = 14
t-3 = ±√14
t = 3 + √14 = appr 6.74 seconds, when it returns to the water
or
t = 3-√14 = -.7416 ???? , see what I mean?