135. Solving a chemistry problem

8. A portion of copper-containing nickel-zinc ferrite weighing m g was dissolved and 100.0 ml of solution was obtained. An aliquot with a volume of Val ml was placed in a separating funnel, the necessary reagents were added and copper was extracted with three portions of 10.0 ml of ethyl acetate. The combined extract was made up to 50.00 ml with ethyl acetate, photometrically and the optical density Ax values ​​were obtained.
Determine the mass fraction (%) of copper in ferrite, using the following data to build a calibration graph, obtained under similar conditions, extracted and photometrically (Vst ml of a CuSO4 standard solution, in which the concentration of copper was 2 μg / ml):
Option 1
m, g 0.2042 Ax0.210 Val, ml 20.0 Vst, ml 10.0 Ast 0.250