Description for Correct answer:
Let rate upstream be kmph

Then, rate downstream = 2x kmph

\( \Large \therefore \) Rate of current

\( \Large \frac{1}{2} (2x - x) = \frac{x}{2} \ kmph \)

\( \Large \therefore \frac{x}{2} = 2 => x = 4 \)

\( \Large \therefore \) Rate upstream = 4 kmph

Rate downstream = 8 kmph

\( \Large \therefore \) Rate in still water

= \( \Large \frac{1}{2} (8 + 4) = 6 \ kmph \)