A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:	Pick one:
A) 10	B) 6	C) 5	D) 4	E) None of these
Explanation:   Speed of the motor boat =15 km/hr   Let speed of the stream =v   Speed downstream =15+v km/hr   Speed upstream =15-v km/hr   Time taken downstream =30/15+v   Time taken upstream =30/15-v   Total time =30/15+v + 30/15-v   Given that total time is 4 hours 30 minutes   =4 1/2hour =9/2hour   ANSWER IS 5
<result>C</result>
A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is: