pre calc world prob

Question

An object is thrown upward at a speed of 107 feet per second by a machine from a height of 15 feet off the ground. The height h of the object after t seconds can be found using the equation h=−16t2+107t+15 

 A.) When will the height be 35 feet?

B.) When will the object reach the ground?

Answer 1

-16t^2 + 107t - 20 = 0

16t^2 - 107t + 20 = 0

t = [ 107 +or- sqrt( 107^2 - 1280)]/32

6.495045616488557

0.19245438351144228