The speed of a train including stoppages is 90 kmph and excluding stoppages is 120 kmph. Of how many minutes does the train stop per hour?	Choose the correct answer:
A) 9	B) 10	C) 12	D) 14	E) 15

Rationale: explanation : t = 30 / 120 * 60 = 15 answer : option e
Answer: E