11. By the method of ultramicroscopy in the flow in the volume W = 1.5 × 10 -11 m 3, 53 spherical particles of an oil mist aerosol were calculated. Determine their average radius, if the concentration of sol C = 21⋅10 -6 kg / m 3; The density of the oil is ρ = 0,92⋅10 3 kg / m 3.