a. When absolute tonne-km is calculated, the travel between any two stations is treated individually.

b. When commercial tonne-km is calculated, the trip is treated as a whole.

A truck starts with a load of 12 tonnes of goods from station X. It unloads 4 tonnes at station Y and rest of the goods at station Z. It reaches back directly to station X after getting reloaded with tonnes of goods at station Z. The distance from X to Y, Y to Z and Z to X are 50 km, 100 km and 120 km, respectively. Compute absolute tonne-km and commercial tonne-km.