Calculate the correct number of moles AND formula units in 7.3x10^-3 g of CaSO4

Avogadro's number represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. This number can be used to convert the number of atoms or molecules into number of moles.

7.3x10^-3 g of CaSO4 (1 mol / 136.14 g) = 5.36x10^6-5 moles

5.36x10^6-5 moles (6.022 x 10^23 formula units / mole) = 3.23x10^19 formula units