An escalator moves towards the top level at the rate of 12 ft.sec and its length is 160 feet. If a person walks on the moving escalator at the rate of 8 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.
A) 10 sec  B) 8 sec  C) 9 sec  D) 7 sec  E) 12 sec

Rationale: "explanation : time taken to cover the entire length = tot . dist / resultant speed = 160 / ( 12 + 8 ) = 8 sec answer : b"
Answer: B