2. The countercurrent speed is equal to the ship speed and water reduction speed.
3. The distance along the river is equal to the speed multiplied by the time along the river.
4. The upstream distance is equal to the upstream speed times the upstream time.
5. The total distance is equal to the distance along the water plus the distance against the water.
6. The total time is equal to downstream time plus upstream time.
7. The average speed equals the total distance divided by the total time.
8. The relative speed is equal to (downstream speed plus upstream speed) divided by 2.
9. The relative speed difference is equal to (downstream speed minus downstream speed) divided by 2.
10, time equals distance divided by speed.
1 1, the distance is equal to the speed times the time.
12, and the distance difference is equal to (downstream speed times downstream time) minus (upstream speed times downstream time).