A small submarine has a volume of 30 m3 and has a mass of 40,000 kg. It needs external tanks that can be filled with air for buoyancy. Assume the compressed air has a density of 37kg/m3 and the seawater has a density of 1030 kg/m3. If the external air tanks have a mass of 2000 kg, what is the minimum volume of the air tanks to provide enough buoyancy to lift the submarine in sea water?