the answer is by adding the vectors.
i (j)hope this
the river current is moving with velocity vc=10 km/h in a certain direction relative to the shore. the boat is moving with velocity vb=10 km/h relative to the current, and in the same direction as the current, so the total velocity of the boat relative to the shore will be equal to the sum of the two vectors (because they are in the same direction):
v=vb+vc = 10 km/h + 10 km/h = 20 km/h
answer; ///i do believe that the correct answer is (b); ///particle composed of two or more atoms bonded together; //////////////