A man can row 9 1 3 kmph in still water and finds that it takes him thrice as much time to row up th...........

Explanation:

Let man’s rate upstream be x km/hr. Then his rate downstream is 3 x km/hr
Given:
Speed in still water = 9 (1/3) = 28/3 km/hr
i.e, ½ (a+b) = 28/3 km/hr
½ (x+3x) = 28/3
2x = 28/3    x = 28/ 2 x 3 = 14/3 km/hr
rate upstream b = 14/3 km/hr and
rate downstream a = 14/3 x 3 = 14 km/hr
speed of the current = ½ (a-b) = ½ (14 – 14/3)
= ½ (42-14/3) = 28/6 = 4 (2/3) km/h