Use the following information to answer questions 6 through 9. A car is traveling with a velocity of 20 m/s when the driver applies the brakes. After 3 seconds, the car's velocity is reduced to 4 m/s. Determine the rate at which the car's velocity is changing.

A) 4 m/s
B) 5 m/s
C) 6 m/s
D) 7 m/s