The height A of an object thrown from a bridge 200 feet high

The height A of an object thrown from a bridge 200 feet high after t seconds is given by h(t) = -16t^2 + 48t + 200. For what times will the object be at least 40 feet high?

Solution

given h(t) = -16t² +48t+200

object to reach atleast 40 feets is

40 = -16t² +48t+200

16t² - 48t - 160 = 0

t² - 3t - 10 =0

(t - 5)(t+2) = 0

t = 5 secns