Use the accompanying table to answer the following questions.
Quantity
Private
Cost Social Cost Benefit
1 $ 2 $ 4 $12
2 $ 6 $ 10 $22
3 $ 12 $ 18 $30
4 $ 20 $ 28 $36
5 $ 30 $ 40 $40
a. What is the external cost per unit of output?
b. What level of output will be produced?
c. What level of output should be produced to achieve economic efficiency?
d. What is the value to society of correcting the externality?