math
posted by Mary on .
Please explain to work this:
A rocket is launched from atop a 105foot cliff with an initial velocity of 156ft/s. the height of the rocket above the ground at time t is given by
h= 16t^2 + 156t + 105. When will the
rocket hit the ground after it is launched? Round to the nearest second.

naturally, when h = 0.
16t^2 + 156t + 105 = 0
t = (39 ± √1941)/8
t = 10 sec 
???????????????????????????????????????Your confusing me! STOP CONFUSING ME!!!!!

h=0, so you set this up in the quadratic formula, which then you follow all the rules and your left with a positive and negative answer. time cant be negative, so the correct answer should be about 10.38 seconds which rounds off to 10.4