Acceleration is equal to the change in velocity per unit time. In this case, velocity has changed from 17.7 m/s to 14.1 m/s, which is a decrease of 3.6 m/s. This takes place in 12 seconds, so the average acceleration is 3.6 m/s / 12s = 0.3 m/s^2. The direction of this acceleration is south, since the car's northbound speed is decreasing.
