one boat is overtaking another which boat must give way?

BoatOnCourse.com – Navigation Rule: Overtaking (full version)

Any vessel overtaking any other vessel must keep out the way of the vessel being overtaken. The former is the give-way vessel and the latter is the stand-on vessel. This rule applies even if the overtaking vessel is propelled by wind, oars, or rubber band paddlewheel.

COLREG Actions Stand On Give Way Vessels – simple IRPCS how to guide