4. The Windsor-Detroit International Freedom Festival hosts one of the largest fireworks displays in the world. The fireworks are set off over the Detroit River. The path of a particular firework rocket is modelled by the relation h=-4.9(t-2)+169.6, where h is the rocket's height above the water, in metres, and t is the time, in seconds.

a) How long will the rocket take to reach its maximum height? What is the maximum height?
b) A firework rocket will stay lit for an average of 5 s. What will the height of a rocket be 5 s after it is launched?