An escalator moves towards the top level at the rate of 12 ft.sec and its length is 150 feet. If a person walks on the moving escalator at the rate of 3 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) 10 sec
B) 20 sec
C) 15 sec
D) 16 sec
E) 14 sec

Rationale: "explanation : time taken to cover the entire length = tot . dist / resultant speed = 150 / ( 12 + 3 ) = 10 sec answer : a"
Answer: A