C02 has an atomic weight of approximately 44 g/mol. Using dimensional analysis:
220 g CO2 / (44 g CO2 / mol) = 220 g CO2 * mol / (44 g CO2) = 5.0 mol CO2. Of course, your school may require more significant figures when calculating atkmic weight so you may have to use 44.0 g/mol or 44.01 g/mol instead of 44 g/mol.
Answer: 5.0 mol (careful with sig figs; read steps carefully please)