13. a. We know that the private costs are $6 to buy a pack of cigarettes. We also know that there is x6 the health damage from this, for a total of $12. Jay is apathetic about purchasing cigarettes at $8. Knowing this, this means that personal costs and advantages must be equal at that price level. The private advantage to Jay of smoking a pack of cigarettes is $8 + $6 = $14 since the personal benefits of this surpass the private costs. b. It is not socially efficient for Jay to smoke a pack of cigarettes. While the social benefits of smoking are equal to the personal benefits (since no one else gets any utility from Jay's smoking), the social benefit of Jay smoking one pack is $14. However, the social costs of Jay's smoking are the aggregate of Jay's costs ($12) and the negative externalities placed on Pcorian society is $5; so, the social expenses of Jay smoking are $17, making it socially inefficient for Jay to smoke a pack of cigarettes. c. Yes, it is now socially efficient for Jay to purchase a pack of cigarettes because the social costs have decreased by $4 while social benefits are unchanged.