3. (15 points) Gruber Ch. 5, Q18, A related question: Gruber Ch. 5, Q9 Suppose that the (external) damage done by pollution is known to be MD = the (private) cost and benefit are given by MC = 100 + 2Q and MB = Do - 2Q precisely known. a) If Do = 1,000, what would be the optimal quantity? What tax would be nece for that to be the equilibrium quantity? b) Suppose that, based on the result from part a, a cap-and-trade system is im