A train 100 meters long takes 6 seconds to cross a man walking at 5 kmph in the direction opposite to that of the train. Find the speed of the train.  Choose the correct option
A) 45 kmph B) 50 kmph C) 55 kmph D) 60 kmph E) 70 kmph

Rationale: "explanation : let the speed of the train be x kmph . speed of the train relative to man = ( x + 5 ) kmph = ( x + 5 ) × 5 / 18 m / sec . therefore 100 / ( ( x + 5 ) × 5 / 18 ) = 6 < = > 30 ( x + 5 ) = 1800 < = > x = 55 speed of the train is 55 kmph . answer : option c"
Answer: C