A motorboat heads upstream a distance of 24 miles on a river whose current is running at 3 miles per hour. The trip up and back takes 6 hours. Assuming that the motorboat maintained a constant speed relative to the water, what was its speed?
9mph is the boat's actual speed. 12mph with the stream and 6mph against the stream. 12mph takes 2 hours to get there and 6mph takes 4 to get back = 6hours.