Answer:
84m
Step-by-step explanation:
Using the kinematics equation we can come up with the answer:

Where:
Vf = final velocity
Vi = initial velocity
t = time
In your problem we have the following given:
Vf= 0 m/s
Vi = 21 m/s
t = 8 seconds
The Vf is zero because the car stopped. The distance given in this case is not useful in determining the car's distance so we will solve it. So just fill in the equation with the given:

Thankfully, the deer was not hit!