can you please explain in detail, I do not understand this

Section: Using Price Incentives in Environmental Regulation Suppose that there are three power-generating plants, all of which generate emissions. The table summarizes the cost of emission reduction for each firm given five different levels of pollution: Tons of smoke emitted per day A 3 2 1 0 Total abatement cost, firm A $14 $30 $50 $75 Total abatement cost, firm B $20 $45 $80 $120 Total abatement cost, firm C $25 $60 $100 $150 Frank - Chapter 10