15. Solving a chemistry problem

1. For the titration of 20.00 ml of water in the presence of an ammonium buffer solution and eriochrome black T, 19.20 ml of 0.0500 mol/l complexone III was used. After addition of NaOH solution and 12.38 ml of the same solution of complexone III to the same portion of water, 12.15 ml of 0.04850 mol/l CaCl2 solution was used for titration of excess complexone III in the presence of murexide. Find the molar concentrations of Ca2 and Mg2 in water.