A company is developing a new additive for gasoline. The additive is a mixture of three liquid ingredients, I, II, and III. For proper performance, the total amount of additive must be at least 11 oz per gal of gasoline. However, for safety reasons, the amount of additive should not exceed 19 oz per gal of gasoline. At least one fourth oz of ingredient I must be used for every ounce of ingredient II, and at least 1 oz of ingredient III must be used for every ounce of ingredient I. The costs of I, II, and III are $0.30, $0.18, and $0.36 per oz, respectively.