Answer:
Permits will be the best option
Explanation:
Assuming the cost per ton of polution reduction follows a linear progression and it can reach zero
The best option will be the permits:
As Firm B will eliminate their polution and sale his permis to Firm A
That occur as Firm B is more efficient in doing this will sale to Firm A
In the end Firm A will have all the permits and continue to produce 200 tons
but Firm B will produce none achieving the goal of 50% reduction with the least economic impact.
This is a market solution which little intervention from the Gvernment
Cost to eliminate 200 polution with permits:
200 x $10 = 2,000
If we force each company to reduce pollution Firm A higher cost will create deadweight-loss
100 x $20 = 2,000
100 x $10 = 1,000
3,000