Q6. A car accelerates from \( 12 \, \text{m/s} \) at \( 1.5 \, \text{m/s}^2 \) for \( 4 \, \text{s} \), then moves at constant speed for \( 5 \, \text{s} \). What is the average speed over the entire motion?
- A. 16 m/s
- B. 17 m/s
- C. 16.67 m/s
- D. 18 m/s