1. **Stating the problem:** Convert the speed of sound from metres per second (m/s) to kilometres per hour (km/h). 2. **Formula and rules:** To convert speed from m/s to km/h, use the conversion factor: $$1\ \text{m/s} = 3.6\ \text{km/h}$$ This is because 1 km = 1000 m and 1 hour = 3600 seconds, so: $$\frac{1000\ \text{m}}{3600\ \text{s}} = \frac{1000}{3600}\ \text{km/s} = \frac{1}{3.6}\ \text{km/s}$$ Therefore, multiply the speed in m/s by 3.6 to get km/h. 3. **Conversion:** Given speed of sound = 340 m/s $$340\ \text{m/s} \times 3.6 = 1224\ \text{km/h}$$ 4. **Next problem:** Two cars start from point S and travel to point D, 140 km away. Car A speed = 100 km/h Car B speed = 80 km/h 5. **Find time taken by Car A to reach D:** $$\text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{140}{100} = 1.4\ \text{hours}$$ 6. **Distance travelled by Car B in 1.4 hours:** $$\text{Distance} = \text{Speed} \times \text{Time} = 80 \times 1.4 = 112\ \text{km}$$ **Final answers:** - Speed of sound in km/h: **1224 km/h** - Distance travelled by Car B when Car A arrives: **112 km**