∵ The train and cyclist are moving in the same direction, Relative speed = 84 – 12 = 72 km/hr. = 72 × 5/18 = 20 m/sec. Now, time taken to cross cyclist = Length of train/relative speed ⇒ 13.5 = Length of train/20 ∴ Length of train = 20 × 13.5 = 270 m