economic question (having trouble)

Suppose the total benefit and total cost to society of various levels of pollution abatement are as follows: Complete column (4). (Enter your responses as integers.) (1) (4) (5) (5) Pollution (2) (3) Total Net Marginal Marginal Abatement Total Benefit Total 605‘ Benefit Benefit Cost 0 o o 0 — — 1 20 9 1 1 2 38 20 18 3 54 33 21 4 68 48 20 5 80 65 15 e 90 84 5 (1) (4) (5) (5) Pollution (2) (3) Total Net Marginal Marginal Abatement Total Benefit Total 605‘ Benefit Benefit Cost 0 0 0 — — 1 20 9 1 1 2 38 20 18 3 54 33 21 4 68 48 20 5 80 65 15 6 90 84 6 Using optimization in levels, if the U.S. Environmental Protection Agency (EPA) wants to maximize total net benefit, then it should require |:| unit(s) of pollution abatement. (Enter your response as an integer.)