2. Suppose there are two firms in the world with marginal costs of abatement given by: MCA = X MCB = 4 Each firm is emitting 10 tons of CO2 initially, for a total of 20 tons. a) What is the marginal cost of abatement for both firms combined (Hint: It will not be a straight line)? What is the combined Xmax? b) Suppose the marginal benefit curve is vertical (a threshold effect) at X = 4. This implies X*=4. What is the cheapest way to reach X* (i.e. how much abatement do A and B do)