7) The following picture shows the private marginal benefit, social marginal benefit, private marginal cost, and social marginal cost for an economy. P 8 PMC -SMC -NWAUO PMB SMB Q 1 2 3 4 5 6 7 8 9 10 14 12 a. (3pts. ) Based on the picture, what kind of externality exits in this economy (positiveegative due to consumption/production)? Explain. b. (3pts.) What is the socially efficient quantity? Also, on the graph below shade the region that corresponds to the maximum possible economic surplus