What mass of the compound CrO3 M1000 contains 45x1023 Oxygen

What mass of the compound CrO3 (M=100.0) contains 4.5x10^23 Oxygen atoms?

Please show me how to get the answer to this problem (i need the steps.)

Solution

no of moles =4.5x10^23/ 6.023*1023 = 0.747 /3 moles = 0.249 moles

mass of the CrO3 =0.249* molar mass = 0.249*100 = 24.9 gms