A rectangular metal box has external dimensions 30 cm × 20 cm × 10 cm and a uniform wall thickness of 0.5 cm. The box is open at the top and the metal has a density of 7800 kg/m³. Dry sand of density 1600 kg/m³ is to be loaded into the box. The box is then slowly lowered, open side up, into freshwater until the rim is just level with the water surface. Calculate the maximum volume of sand, in cm³, that can be placed in the box without causing it to sink.