Answer – B (350 m)
Explanation – when it cross a pole actually it is crossing itself
so, S = 300/18
let length of platform be “p”
relative speed = total lengths/time
speed of train = [300 + p ]/39
(300/18)x39=300 +p
650 -300=p
p=350 m
Note : in this type of question one thing is pole,man and other is of
considerable length like platform ,bridge.
when train crosses pole,man it crosses itself