Question 796166
Weight of the whole buoy = Weight of the water displaced by the submerged portion of the buoy
Volume of the whole buoy = Volume of the water displaced by the submerged portion of the buoy
Volume of the whole buoy = Volume of submerged portion of the buoy


Continue along the above line and you will find the answer.
P.S.: This problem follows from the Archimedes' principle of buoyancy.