Suppose the dollar amount of the externality, per gallon of gasoline, is constant, regardless of how much gasoline is produced. Then the externality could be internalized if producers of gasoline were a. required to pay a tax of $0.45 per gallon of gasoline sold.
b. provided a subsidy of $0.45 per gallon of gasoline sold.
c. required to pay a tax of $0.30 per gallon of gasoline sold.
d. provided a subsidy of $0.30 per gallon of gasoline sold.