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 4t seconds, then what is the length of the platform?  Choose the correct choice from the following answers:
A) 0.5 l
B) l
C) 1.5 l
D) 2 l
E) 3 l

Rationale: "the train passes a pole in t seconds , so velocity v = l / t ( l + p ) / v = 4 t ( l + p ) / ( l / t ) = 4 t p = 3 l the answer is e ."
Answer: E