113. Solving a chemistry problem

A portion of 5.00 g of apatite was boiled with aqua regia, the solution was transferred into a 500 ml volumetric flask and brought to the mark. 10 ml of the solution was taken from the volumetric flask and PO43- was precipitated as ammonium phosphate-molybdate. 50 ml of 0.200 M KOH solution was added to the precipitate, and 25.63 ml of 0.2021 N H2SO4 solution was used for titration of excess alkali. Calculate the mass fraction of P2O5 in the apatite sample.