1. **Problem (a):** Sara rides her bicycle at a speed of 420 metres per minute. We need to convert this speed to kilometres per hour (km/h). 2. **Formula and rules:** - To convert metres per minute to kilometres per hour, use the conversion factors: - 1 kilometre = 1000 metres - 1 hour = 60 minutes 3. **Conversion steps:** - Sara's speed in metres per minute is 420. - Convert metres to kilometres: $\frac{420}{1000} = 0.42$ km per minute. - Convert minutes to hours: multiply by 60 to get km/h. 4. **Calculation:** $$\text{Speed in km/h} = 0.42 \times 60 = 25.2$$ 5. **Answer for (a):** Sara's speed is **25.2 km/h**. 6. **Problem (b):** Jan cycles 51 km, starting at 11:55, finishing at 14:41, with a 25-minute rest stop. Calculate her average cycling speed in km/h (excluding rest). 7. **Calculate total time elapsed:** - From 11:55 to 14:41 is 2 hours and 46 minutes. - Convert to minutes: $2 \times 60 + 46 = 166$ minutes. 8. **Subtract rest time:** - Cycling time = $166 - 25 = 141$ minutes. - Convert cycling time to hours: $\frac{141}{60} = 2.35$ hours. 9. **Calculate average speed:** - Average speed = $\frac{\text{distance}}{\text{time}} = \frac{51}{2.35} \approx 21.7$ km/h. 10. **Answer for (b):** Jan's average cycling speed is approximately **21.7 km/h**.