Two trains of length 100 m and 200 m are running towards each other on parallel lines at 42 kmph and 30 kmph respectively. In what time will they be clear of each other from the moment they meet? Choose the correct choice from the following choices:
A) 18 sec
B) 15 sec
C) 21 sec
D) 20 sec
E) 19 sec

Rationale: "relative speed = ( 42 + 30 ) * 5 / 18 = 4 * 5 = 20 mps . distance covered in passing each other = 100 + 200 = 300 m . the time required = d / s = 300 / 20 = 15 sec . answer : b"
Answer: B