Two trains of equal length are running on parallel lines in the same direction at 46 km/hr and 36 km/hr. The faster train catches and completely passes the slower train in 72 seconds. What is the length of each train (in meters)? Pick one.
A) 70	B) 80	C) 90	D) 100	E) 110

Rationale: "the relative speed = 46 - 36 = 10 km / hr = 10 * 5 / 18 = 25 / 9 m / s in 72 seconds , the relative difference in distance traveled is 72 * 25 / 9 = 200 meters this distance is twice the length of each train . the length of each train is 200 / 2 = 100 meters the answer is d ."
Answer: D