The velocity of a passenger relative to a boat is -vpb. The velocity of the boat relative to the river it is moving on is vbr. The velocity of the river to the shore is vrs. What is the velocity of the passenger relative to the shore
If the passenger were at rest, his speed relative to the shore will be identical to the boat's, as follows:
vps = vbr + vrs
As he is moving in a direction opposite to the boat's, his velocity relative to the shore must be less than if he were at rest, in the same quantity that he was moving opposite to the boat, as follows: