Chapter 3.4, Problem 155E

The position function $s\left(t\right)=t^2-3t-4$ represents

the position of the back of a car backing out of a driveway and then driving in a straight line, where s is in feet and t is in seconds. In this case, $s\left(t\right)=0$ represents the time

at which the back of the car is at the garage door, so $s\left(0\right)=-4$ is the starting position of the car, 4 feet inside the garage.

Determine the velocity of the car when $s\left(t\right)=0$ .

Determine the velocity of the car when $s\left(t\right)=14$