Instantaneous Velocity Sample Problem

1. A car is stopped at a traffic light. It then travels along a straight road so that its distance from the light is given by  (a) x(t)=bt^2-ct^3, where b=2.40m/s^2 and c=0.120m/s^3.   Calculate the average velocity of the car for the time interval to (b) Calculate the instantaneous velocity of the car at and (c) How long after starting from rest is the car again at rest?
Answer: