Titration of Ca+2 and Mg+2  in a  150 mL sample of hard water required  75 mL of 0.0125 M  EDTA. A second 100 mL aliquot was made strongly basic with NaOH to precipitate Mg+2 as Mg(OH)2(s). The supernatant liquid was titrated with 28.5 mL of the EDTA solution. Calculate the ppm Mg2+. 