68. Solving a chemistry problem

4. To determine the content of furadonin in the drug, a sample of this drug weighing 0.01018 g was dissolved in water; the volume of the solution was brought to 50 ml. In two volumetric flasks with a capacity of 100 ml each, 10 ml of the resulting solution was taken. 0.00255 g of pure furadonin was added to one of them. The solutions in the flasks were diluted with water to the mark. The optical densities of these two solutions, measured at λ=360 nm in a cell 1 cm thick, turned out to be 0.19 and 0.46. Calculate the mass fraction of furadonin in the preparation.