Two trains 180m and 360m long run at the speed of 60kmph and 30kmph in opposite directions in parallel tracks. The time which they take to cross each other is?
Choose one: A) 21.6 sec B) 8.9 sec C) 10.8 sec D) 12.6 sec E) 15 sec

Rationale: "relative speed = 60 + 30 = 90 kmph * 5 / 18 = 25 m / s distance covered in crossing each other = 180 + 360 = 540 m required time = 540 * 1 / 25 = 21.6 sec answer is a"
Answer: A