A river current has a velocity of 10 km/h related to the shore in a boat moves in the same direction as a current of 10 km/h related to the ripper how can the velocity of the boat related to the shore be calculated

It would be 20 km/hr. Because the current and the boat are moving in the same directions, the velocity can be added relative to the shoreline. The shoreline isn't moving so the person looking would see the boat going at 20 km/hr because the current is already making it look like it's going 10 km/hr.