An escalator moves towards the top level at the rate of 15 ft.sec and its length is 200 feet. If a person walks on the moving escalator at the rate of 5 feet per second towards the top level, how much time does he take to cover the entire length.
Choose the most appropriate option:
A) 5 sec	B) 10 sec	C) 20 sec	D) 15 sec	E) 25 sec

Rationale: "explanation : time taken to cover the entire length = tot . dist / resultant speed = 200 / ( 15 + 5 ) = 10 sec answer : b"
Answer: B