Excluding stoppages, the speed of a train is 42 kmph and including stoppages it is 27 kmph. Of how many minutes does the train stop per hour? Answers
A) 19.42
B) 20.42
C) 21.42
D) 22.42
E) 23.42

Rationale: "explanation : t = 15 / 42 * 60 = 21.42 answer : option c"
Answer: C