A train passes a station platform in 36 seconds and a man standing on the platform in 20 seconds. If the speed of the train is 54 km/hr, what is the length of the platform?

Answer: Option B

Speed = $$\left(54\times \frac{5}{18}\right)$$  m/sec = 15 m/sec
Length of the train = (15 × 20) m = 300 m
Let the length of the platform be x meters
Then, $$\frac{\text{x}+300}{36}$$  = 15
⇒ x + 300 = 540
⇒ x = 240 meters