Ashutosh can row 24 km/h in still water. It takes him twice

Ashutosh can row 24 km/h in still water. It takes him twice as long to row up as to row down the river. Find the rate of stream. ?

Let rate of stream be 'a' km/h.
According to the question.
24 + a = 2(24 - a)
⇒ 24 + a = 48 - 2a
⇒ 3a = 48 - 24 = 24
∴ a = 24/3 = 8 km/h