A 1.000-mL aliquot of a solution containing Cu2 and Ni2 is treated with 25.00 mL of a 0.04978 M EDTA solution. The solution is then back titrated with 0.02398 M Zn2 solution at a pH of 5. A volume of 15.45 mL of the 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 passed through the column is treated with 25.00 mL 0.04978 M EDTA. This solution required 20.08 mL of 0.02398 M Zn2 for back titration. The Ni2 extracted from the column was treated witn 25.00 mL of 0.04978 M EDTA. How many milliliters of 0.02398 M Zn2 is required for the back titration of the Ni2 solution?