A phosphorus oxide has an empirical formula of PxOy and 56.36% phosphorus by mass . What is the values of x anf y?

moles of P in 100 g of the oxide = 56.36 / MM of P = 56.36 / 30.97 = 1.820 moles
mass of O in 100 g = 100-56.36 = 43.64 g or 43.64 / 16 moles = 2.73 moles

molar ratio of P:O = 1.820: 2.73
to simplify the ratio we divide by the smaller number and we get 1:1.5
now we multiply by 2 to get whole number ratios ... 2:3

empirical formula is P2O3