075. Solving a chemistry problem

12. 10 ml of furatsilin solution was taken into a 100 ml flask and the volume of the solution was brought to the mark with distilled water. In two volumetric flasks with a capacity of 50 ml, 10 ml of the resulting solution was taken and 10 ml of 0.5 M NaOH was added. 5 ml of a standard solution of furatsilin with a concentration of 10 μg/ml was added to one flask and the volume of both flasks was adjusted to the mark with water. The optical densities of the solutions measured after 15 minutes at a wavelength of 440 nm are equal to A(X)=0.390 A(x+st)=0.530. Calculate the content of furatsilin (in%) in the analyzed solution.