Purification & Characterisation · Phosphorus estimation as pyrophosphate

By usual analysis, 1.00g of compound (X) gave 1.79g of magnesium pyrophosphate. The percentage of phosphorus in compound (X) is: (nearest integer)

(Given, molar mass in g mol$^{-1}$: O $= 16$, Mg $= 24$, P $= 31$)