If an egg is thrown up and off the roof of a 100 foot building with an initial upward velocity of 10 feet per second, how long until it hits the ground?

The equation of the height as a function of time for this case is given by:
 h (t) = - 16t ^ 2 + 10t + 100
 By the time the egg hits the ground we have:
 -16t ^ 2 + 10t + 100 = 0
 We look for the roots of the polynomial:
 t1 = -2.2069555463432966
 t2 = 2.8319555463432966
 As it is about time, we use the positive root:
 t = 2.83 s
 
 it hits the ground at:
 t = 2.83 s