Final answer:
The socially efficient tax for the industry can be calculated by equating the MAC and MDC. The equilibrium quantity E is found by solving the equation 180 - 2E = 4E. The socially efficient tax is $120.
Step-by-step explanation:
The socially efficient tax for an industry can be calculated by equating the marginal abatement cost (MAC) to the marginal damage cost (MDC). In this case, the MAC is given by the equation MAC = 180 - 2E and the MDC is given by MDC = 4E. To find the socially efficient tax, we need to find the value of E at the equilibrium where MAC equals MDC.
Equating MAC and MDC:
180 - 2E = 4E
180 = 6E
E = 30
Substituting the value of E back into the MAC equation:
MAC = 180 - 2(30) = 120
Therefore, the socially efficient tax is $120 (option B).