Given the number of a substance , how do you solve for the number of a moles of a substance

Given the number of a substance, we can solve the number of moles by using a conversion factor that would relate the number of a substance to the number of moles. In any case, Avogadro's number would be used. It 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. For example, we are given 1.23 x 10^24 atoms of a substance converting it to moles we do as follows:

 1.23 x 10^24 atoms ( 1 mol / 6.022x10^23 atoms ) = 2.04 moles

The answer should be c.