Excluding stoppages, the speed of a train is 30 kmph and including stoppages it is 21 kmph. Of how many minutes does the train stop per hour? Choose the correct option.
A) 16
B) 17
C) 12
D) 15
E) 18
T = 9/30 * 60= 
<gadget id="calculator">9/30 * 60</gadget>
<output>18</output>
18   Answer: 18
<result>E</result>
Excluding stoppages, the speed of a train is 30 kmph and including stoppages it is 21 kmph. Of how many minutes does the train stop per hour?