1\ The time required for a ship to sail 80km downstream is the same as that required for sailing 60km upstream. Given that the speed of the ship in still water is 2 1km/h, find the current speed.

2\ In the triangle ABC, AB=AC=5 and BC=8, find the high AD on the side of BC.

3\ It is known that y=y 1+y2, y 1 is proportional to x, y2 is proportional to x- 1, and y = 4； when x=3; When x= 1 and y=2, find the functional relationship between y and X.