123. Solving a chemistry problem

13. To 10 ml of a solution containing calcium, 10 ml of a solution of H2C2O4 was added, the excess of which was titrated with 4.25 ml of a solution of potassium permanganate with a concentration of c(1/5KMnO4)=0.1040 mol/l. For 1 ml of H2C2O4 solution during titration, 1.02 ml of KMnO4 solution is consumed. Determine the mass fraction (%, mass) of calcium in the analyzed solution.