Guards patrolling a mall protect the mall's two stores. The electronics store's demand curve for guards is greater at all prices than that of the ice cream parlor. The marginal cost of a guard is $10 per hour. Use a diagram to show the equilibrium, and compare that to the socially optimal equilibrium. Now suppose that the mall's owner will provide a subsidy of s per-hour-per-guard. Show in your graph the optimal s that leads to the socially optimal outcome for the two stores?