Consider two firms with the following marginal abatement costs (MAC) as a function of emissions (E):

MAC_1 = 18 - 2E_1

MAC_2 = 12 - E_2,

and assume marginal external damages (MED) from the aggregate emissions of both firms (E_Agg = E_1 + E_2) is:

MED = .5E_Agg.

To achieve the socially efficient level of aggregate emissions (E*_Agg), the government institutes a per-unit tax on emissions. In principle, firms could continue to emit pollution as they were in the absence of government intervention, but by cutting back on emissions, their total compliance costs (tax payment plus total abatement costs) goes down. How much money can firms save if they reduce their emissions to E*_Agg in response to the tax?