123. Solving a chemistry problem

24. A weighing m (g) of brass was dissolved in nitric acid, and after separation of tin, iron and lead, the filtrate was diluted to 250.0 ml. An equal volume of supporting electrolyte (ammonium buffer and gelatin) was added to an aliquot V(ml) of the solution, and after removal of air, polarography was performed.
The diffusion current at E=-0.6 V corresponds to the reduction of copper (Id,Cu), and at E=-1.4 V to the reduction of zinc and nickel (Id, Zn+Ni). To another aliquot V(ml) were added solutions of Na2SO3, KCN, gelatin, ammonium buffer with a total volume of 20.0 ml. The polarogram of this solution gives only a nickel wave with the value Id, Ni.
OPTION 1
Sample, m, g 0.4500
Aliquot V, ml 20
Diffusion current, µA
Id,Cu 53.40 58.63 68.25
Id, Zn+Ni 24.18 25.73 27.38
Id, Ni 0.79 0.85 1.04
Calculate the mass fraction of % Cu, Zn, Ni in brass if, under the selected measurement conditions, the diffusion current constants Id / C (μA / mmol) are equal: for copper 6.54, for zinc and nickel 4.23, for nickel 4.85. The measurement results are shown in the table.