Kramer and Newman hatch a scheme to arbitrage bottles from NY, where the deposit is 5 cents, to Michigan, where the deposit is 10 cents. They can't figure out how to make the costs work; gas is too expensive (variable costs), and there's too much overhead (fixed costs of tolls, permits, etc.) with using a semi to haul the bottles in volume. Finally, they hatch a scheme to use a mail truck, which lowers their variable and fixed costs to zero.