4. Figure below shows a market with a negative externality. Price 52 = Marginal social cost 81 = Marginal Pl .............................................................. _ private cost Pa - Pb . Po .................................................. Demand 0 0d 0a Ob Quantity 4.1 What is the efficient output level? 4.2 By which area is the deadweight loss due to the externality represented? 4.3 By which price is the marginal benet of the last unit produced represented