Answer:
$380
Explanation:
                      Firm A      Firm B     Firm C
1st unit of pollution        $20       $50       $500
2nd unit of pollution       $60       $100       $700
3rd unit of pollution       $120       $180      $1,000
4th unit of pollution      $200       $350      $1,500
5th unit of pollution      $300       $500     $2,500
6th unit of pollution      $400       $600     $4,000
Firm A's cost of eliminating four units of production = the sum of the costs of eliminating the four units = $20 (for the first unit) + $60 (for the second unit) + $120 (for the third unit) + $200 (for the fourth unit) = $380
This table does not show cumulative costs, instead it shows the marginal costs of eliminating an extra unit of pollution.
