algebra 2 question read description

Question

A model rocket is launched with an initial velocity of 160 ft/s. The height, h, in feet, of the rocket t seconds after the launch is given by h = −16t² + 160t.

 How many seconds after launch will the rocket be 320 ft above the ground? What is the smaller and larger value?

Answer 1

320 = -16t^2 + 160t

divide by -16 to get

t^2 -10t +20 = 0

t=5+ or - (1/2)sqr20 = about 2.8 and 7.2 seconds