It was already late when we set out for the next town, which according to the map was about fifteen kilometers away on the other side of the hills. There we felt that we would find a bed for the night. Darkness fell soon after we left the village, but luckily we met no one as we drove swiftly along the narrow winding road that led to the hills. As we climbed higher, it became colder and rain began to fall, making it difficult at times to see the road. I asked John, my companion, to drive more slowly. After we had travelled for about twenty kilometers, there was still no sign of the town which was marked on the map. We were beginning to get worried. Then without warning, the car stopped and we found we had run Out of petrol.
The travellers were worried after twenty kilometers because
The passage explicitly states, "After we had travelled for about twenty kilometers, there was still no sign of the town which was marked on the map. We were beginning to get worried." The map indicated the town was approximately fifteen kilometers away. Therefore, having traveled five kilometers beyond the expected distance without reaching the town, the travellers' worry is directly attributable to the probability of having lost their way, as the expected landmark was absent.