A boat goes 6 km in an hour in still water. It takes thrice as much time in covering the same distance against the current. Speed of the current is_______?

A. 2 km/hr
B. 3km/hr
C. 4km/hr
D. 5 km/hr
Explanation:
Speed in still water = 6 km/hr
Speed against the current = 6/3 km/hr = 2 km/hr
Let the speed of the current be x km/hr
6-x = 2 => x =4 km/hr