osmotic pressure

Use the fact that a mole of water has a mass of 18 grams, and therefore occupies a volume 18 cm3, to calculate the volume per water molecule, ?. Use this to calculate the osmotic pressure corresponding to a decrease in 0.001 eV in chemical potential experienced by water as it goes from pure water to a salt solution. How far beneath the surface of the ocean would you have to be for the pressure to be this large? (Pressure increases with depth at a rate of 1 atm per 10 meters of depth.)