Science and Medicine - Math Word Problem?

Question

The equation h = -16t^2 + 112t

This gives the hieght of an arrow, shot upward from the ground with an intial velocity of 112 ft/s , where t is the time after the arrow leaves the ground. I have to find the time it takes for the arrow to reach a hieght of 120 ft ??

Please help !

Answer 1

120 = -16t^2 + 112t

0 = -16t^2 + 112t - 120

0 = 2t^2 - 14 + 15

t = (14 + (14^2 - 4(2)(15))^.5) / 4
t = 5.67945 seconds

Answer 2

120=-16t^2+112t
dividing by 8
15=-2t^2+14t
=>2t^2-14t+15=0
t=[14+/-sq.rt(196-120)]/4
=(14+6.78)/4
=5.2 sec