1. **State the problem:** Convert 54 miles per gallon (mpg) into kilometres per litre (km/L). 2. **Given conversions:** - 5 miles = 8 kilometres - 2 gallons = 9 litres 3. **Convert miles to kilometres:** Since 5 miles = 8 km, 1 mile = \frac{8}{5} km. 4. **Convert gallons to litres:** Since 2 gallons = 9 litres, 1 gallon = \frac{9}{2} litres. 5. **Calculate 54 miles per gallon in km per litre:** $$54 \text{ miles/gallon} = 54 \times \frac{8}{5} \text{ km} \div \frac{9}{2} \text{ litres}$$ 6. **Simplify the expression:** $$= 54 \times \frac{8}{5} \times \frac{2}{9} \text{ km/litre}$$ 7. **Calculate step-by-step:** $$54 \times \frac{8}{5} = \frac{54 \times 8}{5} = \frac{432}{5} = 86.4$$ $$86.4 \times \frac{2}{9} = \frac{86.4 \times 2}{9} = \frac{172.8}{9} = 19.2$$ 8. **Final answer:** $$54 \text{ mpg} = 19.2 \text{ km/litre}$$ This means 54 miles per gallon is equivalent to 19.2 kilometres per litre.