10. A rollercoaster reaches a top speed of 117 km/hr. Its initial (and tallest)
descent can be modeled by h(t) = 81–4.9t2 , where h is in meters and
t is in seconds. Use this information to solve the following questions:
a How long before the roller coaster reaches the ground?
b) What is the height of the roller coaster just before it begins its decent?
c) Draw a graph to show the decent of the rollercoaster. Include the
coordinate points of the x and y axis.

help!