Final answer:
The car was moving for 12 seconds.
Step-by-step explanation:
To determine the length of time the car was moving, we can divide the distance it traveled by its average velocity. In this case, the car traveled 18 meters south at an average velocity of 1.5 m/s south. Therefore, the time can be calculated as:
Time = Distance / Velocity
Time = 18 m / 1.5 m/s = 12 seconds
So, the car was moving for 12 seconds.