7.1. A truck and a car are moving in the same direction on adjacent lanes at speeds of 65 km/h and 85 km/h, respectively. At what distance from each other will they be 3 minutes after they are side by side?
Answer: 1 km. Solution. The difference in the speeds of the cars is 20 km/h, so in 3 minutes they will be separated by a distance equal to 20 (km/h) $\cdot \frac{1}{20}$ (hour) $=1$ km.