This principle states that the buoyancy force equals the weight of the water displaced by the body

Question:

This principle states that the buoyancy force equals the weight of the water displaced by the body (partly or totally submerged). The cylindrical buoy of diameter 60cm in Fig. 42 is floating in water with its axis vertical. When depressed downward in the water and released, it vibrates with period 2 sec. What is itsweight?