Ell. The velocity of a car decreases from 28 m/s to 20 m/s in a time of 4 seconds. What is the average acceleration of the car in this process? (See example box 2.3.) E12. Starting from rest, a car accelerates at a rate of 6.7 m/s for a time of 4 seconds. What is its velocity at the end of this time? (See example box 2.4a.) E13. A car traveling with an initial velocity of 27 m/s slows down at a constant rate of 5.4 m/s2 for 3 seconds. What is its velocity at the end of this time