The South Johnston tennis team goes through a dozen tennis balls every week (on average). If they want to always have at least a week's supply on hand, and it takes a
week to get more tennis balls, how low can their supply get before they should reorder?

B. 20 fewer tons of pollution into the air, and Firm B will emit 100 fewer tons of pollution into the air.

Explanation:

If Firm B uses the pollution permits as assigned, it would have to spend $6000 for pollution elimination (60 tons, $100 each). If Firm A uses only the pollution permits assigned, it would have to spend $12000 for pollution elimination (60 tons, $200 each).

However, if firm B sells all 40 permits to firm A, as long as the value of each permit is higher than $100 and lower than $200, firm B could make a profit, and firm A could save money.

In that case, firm A could emit 80 tons of pollution into the air, and firm b could avoid emitting any pollution.