algebra rocket question

Question

a model rocket launched from a platform 2 feet above the ground with an upward velocity of 100 feet per second after how many seconds will the rocket hit the ground?

Answer 1

x(t) = -16t^2 + 100t + 2

Note that at time t=0, the rocket is already 2 feet above the ground prior to launch

-16t^2 + 100t + 2 = 0

-8t^2 + 50t + 1 = 0

8t^2 - 50t - 1 = 0

t = [50 +or- sqrt( 2500 + 32)]/16

t = [50 +or- sqrt( 2532)]/16

or approximately 6.27 seconds