An escalator moves towards the top level at the rate of 12 ft.sec and its length is 210 feet. If a person walks on the moving escalator at the rate of 2 feet per second towards the top level, how much time does he take to cover the entire length.	Choose the correct choice from the following answers:
A) 15 sec  B) 10 sec  C) 12 sec  D) 8 sec  E) 9 sec

Rationale: "time taken to cover the entire length = tot . dist / resultant speed = 210 / ( 12 + 2 ) = 15 sec answer : a"
Answer: A