A 1.000- mL aliquot of a solution containing Cu2+ and Ni2+ is treated with 25 mL of a 0.04446 M EDTA solution. The solution is then back titrated with 0.02119 M Zn2+ solution at a pH of 5. A volume of 15.14 mL of Zn2+ solution was needed to reach the xylenol orange end point. A 2.000-mL aliquot of the Cu2+ and Ni2+ solution is fed through an ion-exchange column that retains Ni2+. The Cu2+ that passses through the column is treated with 25 mL 0.04446 M EDTA. This solution required 23.29 mL of 0.02119 M Zn2+ for back titration. The Ni2+ extracted from the column was treated with 25 mL of 0.04446 M EDTA. How many milliliters of 0.02119 M Zn2+ is required for the back titration of the Ni2+ solution?