Solve for the efficient level of abatement (A) and compute the values of MSB and MSC at this efficient level of abatement. Question 3 options: A = 12 percent; MSB = $20 million; MSC = $20 million A = 20 percent; MSB = $15 million; MSC = $15 million A = 12 percent; MSB = $15 million; MSC = $15 million