Two Firms,A and B,each Currently Dump 50 Tonnes of Chemicals

Two firms,A and B,each currently dump 50 tonnes of chemicals into the local river.From now on both firms will require a pollution permit for each tonne of pollution dumped.It costs Firm A $100 for each tonne of pollution that it eliminates before it reaches the river,and it costs Firm B $50 for each tonne of pollution that it eliminates before it reaches the river.The government gives each firm 20 pollution permits.What is the total cost of reducing pollution if the firms are NOT allowed to buy and sell pollution permits from each other,and,NOT including the cost of buying

A) $3000
B) $3500
C) $4000
D) $4500