A train of length L is traveling at a constant velocity and passes a pole in t seconds. If the same train travelling at the same velocity passes a platform in 3.5t seconds, then what is the length of the platform?  Choose the correct choice: A) 0.5 l B) 1.5 l C) 2.5 l D) 3.5 l E) 4.5 l

Rationale: "the train passes a pole in t seconds , so velocity v = l / t ( l + p ) / v = 3.5 t ( l + p ) / ( l / t ) = 3.5 t p = 2.5 l the answer is c ."
Answer: C