Answer:
Firm A will buy all of the firm B's pollution permits. Each one will cost between $100 and $200.
Step-by-step explanation:
The firm B will gain from the trade of pollution permits. Firm A will need higher pollution permits since it emits 100 tons of chemicals into air and the cost for eliminating each ton is $200. This cost is higher than the cost to Firm B which is $100 only. Firm A will buy all the pollution permits from Firm B and there will advantage for the Firm B to gain from the trade.