1. The problem asks to find 15% of 120 kilometres. 2. To find a percentage of a number, use the formula: $$\text{Percentage value} = \frac{\text{Percentage}}{100} \times \text{Total value}$$ 3. Here, the percentage is 15 and the total value is 120 kilometres. 4. Substitute the values into the formula: $$15\% \text{ of } 120 = \frac{15}{100} \times 120$$ 5. Simplify the fraction by canceling common factors: $$\frac{\cancel{15}}{\cancel{100}} \times 120 = \frac{3}{20} \times 120$$ 6. Multiply the fraction by 120: $$\frac{3}{20} \times 120 = 3 \times \frac{120}{20} = 3 \times 6 = 18$$ 7. Therefore, 15% of 120 kilometres is 18 kilometres.