Applications of quadratics. Toy rocket

Question

 A toy rocket is launched from a platform 4.2 m above the ground in such a way that is height, h (in meters) after t seconds is given by the equation 

h = -4.9t² + 28.7t +4.2  How long will it take for the rocket to hit the ground ? 

The rocket will hit the ground after___ seconds

Answer 1

Set h(t) = 0 and solve for t.  You should get a negative and a positive solution for t.  Since t starts at t = 0, discard the negative solution.  You should get t = 6s.