Description for Correct answer:
Speed of current = x kmph

Rate downstream of boat B = (10 + x) kmph

Speed of boat A in still water = (10 + x)kmph

\( \Large \therefore \) Rate upstream

= 10 kmph

According to the question,

\( \Large \frac{40}{10} - \frac{24}{10 + x} = 2 \)

=> \( \Large \frac{24}{10 + x} = 4 - 2 = 2 \)

=> 10 + x = 12

=> x = 2 kmph

\( \Large \therefore \) Speed of boat A in still water

= 10 + 2 = 12 kmph