A man rows 12 km in 5 hours against the stream, the speed of current being 4 kmph. What time will be taken by him to row 15 km with the stream?

Let the speed of the man in still water = 'm' kmph

Speed of current(s) = 4 kmph

Upstream Speed = $$\frac{12.5}{5}=2.4$$ kmph

$$=$$>  m-s = 2.4

$$=$$>  m-4 = 2.4

$$=$$>  m = 6.4 kmph

$$\therefore\ $$Downstream speed = m+s = 6.4+4 = 10.4 kmph

Time taken by the man to row 15 km with stream =$$\frac{15}{Downstream\ Speed}=\frac{15}{10.4}=\frac{75}{52}=1$$ hr$$+\frac{23}{52}\times60\min=1$$ hr$$ \frac{345\ }{13}\min$$

Hence, the correct answer is Option C