A lorry passes a checkpoint at 45 km/h. Eight minutes later, a car passes the same checkpoint at 72…

Step 1. The head start. $12.5\ \text{m/s} \times 480\ \text{s} = 6000\ \text{m}$.

Step 2. The catch. The gap closes at $20\ \text{m/s} - 12.5\ \text{m/s} = 7.5\ \text{m/s}$, so $t = \dfrac{6000\ \text{m}}{7.5\ \text{m/s}} = 800\ \text{s} = 13.33\ \text{min}$.

Step 3. Where. $20\ \text{m/s} \times 800\ \text{s} = 16\,000\ \text{m} = 16\ \text{km}$.