posted by Anonymous .
You are riding in a boat whose speed relative to the water is 4.7 m/s. The boat points at an angle of 24.4° upstream on a river flowing at 13.1 m/s. Find the time it takes for the boat to reach the opposite shore if the river is 25.9 m wide.
the cross-stream speed is 4.7 cos 24.4° = 4.29m/s
So, it takes 25.9/4.29 = 6.04 sec
The speed of the river does not matter, unless you want to find how far upstream or downstream the boat lands.