Motor Daddy: It's convenient for you not to respond to what I wrote. I see that. You'll make just about any excuse to avoid facing up to your absurdities. Just to be clear on your position: Would it be possible, in your opinion, to determine the speed of the current if you only know the boat's speed in calm water and the time taken for the boat to travel a known distance along the embankment (in the current, not in calm water)? If so, how would you do it? And can you show us how your method would apply to the question given in the opening post? Also: would it be possible to calculate in advance how far the boat would move along the embankment in a given time, if you knew the speed of the current and the boat's speed in calm water? If so, how would you do that?