If a man takes 2 hrs either to row 7 km upstream or 15 km downstream, the speed of the current in (kmph) is:

The correct answer is (b).

The speed of the current is equal to half the difference between the speed upstream and the speed downstream.

Speed upstream = 7/2 = 3.5 km/h
Speed downstream = 15/2 = 7.5 km/h
Speed of the current = (7.5 – 3.5)/2 = 2 km/h

Option (a) is incorrect because the speed of the current cannot be less than 0.
Option (c) is incorrect because the speed of the current cannot be greater than the speed downstream.
Option (d) is incorrect because the speed of the current cannot be greater than the speed upstream.