60-20 = 40m (countercurrent speed)
The speed ratio of downstream and upstream = 80: 40 = 2: 1.
Time ratio between downstream and upstream = 1: 2
3: 30 = 2 10
2 10/( 1+2) = 70 minutes (water use time)
70 * 80 = 5600 meters (a * * * distance)