Question

A river flows at a velocity of 3 km/h relative to the riverbank. A boat moves downstream at a velocity of 15 km/h relative to the river. What is the velocity of the boat relative to the riverbank?

Answer 1

15+3=18km/hour
Think about it like this. The boat is going 15 faster than the river, and the river is going 3 faster than the bank, so the boat is going 18 faster than the river bank