RBI Grade B Officers 22 Nov 2015 Paper

A boat takes 3 hours less time in rowing from point X to point Y in downstream than that in rowing from point Y to point Z in upstream. The distance between X and Y is 20 km which is half of the distance between Y and Z. Speed of boat B in still water is 10 kmph. The speed of boat A in still water is equal to the rate upstream of boat B. What is the speed of boat A in still water? (in kmph).