There are two power generating firms A and B in a country "Elec-land". Carbon will be emitted in power generating process. Current level of carbon emissions is 150 for A and 100 for B. Marginal cost of carbon emission reduction for two firms are as follows. MCA = 39A + 30 MCB = 2qg + 20 where q is the amount carbon emission reduction. Marginal benefit of emissions reduction is estimated to be MB = 200-2q To reduce the carbon emission, a government is considering emission fee or cap-and-trade scheme. (a) What is the socially optimal level of emissions reduction? (b) If emissions fee is set at 120, what is the amount of emissions reduction?