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. And with the molar mass from moles to mass.
9.86×1024 molecules CO2 ( 1 mol / 6.022x10^23 molecules ) ( 44.01 g / 1 mol ) = 720.59 g CO2