140. Solving a chemistry problem

In the study by the Deryagin-Vlasenko method of flow ultramicroscopy of the oil aerosol, an average of 50 particles were found in a volume of 1.33 * 10-5 cm3, which passed through the counting field of the microscope. Calculate the radius of the aerosol droplets, knowing its concentration 25.0 mg / m3 and the density of the oil 0.910 g / cm3.