The weight of the cube is balannced by the huoyant force. The buoyant force is equla to the wieght of the water displaced. If a volume V of the cube is inside the water the weight of the displaced water `=Vrhog`. Where rho is the density of water thus.
`Vrhog=(0.7kg)g`
`V=(0.7kg)/rho=(0.7kg)/(1000kgm^-3)=7xx10^-4m^3=700cm^3`
the total volume of the cube `=(10cm)^3=1000cm^3`
The volume outside the water is
`1000cm^3-700cm^3=300cm^3`
