Question 461149
Let b = speed of the boat in still water, and s = speed of the stream.

Then 3(b-s) = 20 for upstream travel, and
and 1.5(b+s) = 20 for downstream travel.

==> b - s = 20/3 and b+s = 40/3, or

b = 10 kph.

b + s = 40/3 ==> s = 10/3 kph.