Suppose that a small company is thinking of putting plants in their lobby for employees to view and enjoy. Since the plants are to be viewed by employees, the plants are non-excludable (it is infeasible to move a plant each time a specific individual walks by) and non-rival in consumption (if one worker looks at the plant, it does not prevent another from doing so as well). The company employs three workers: Tim, Greg, and Sharon. The company is thinking about buying up to three plants, and wants to know how much workers would enjoy each plant. For Tim, the first plant has a benefit of $31 per day, the second plant has a benefit of $19 per day, and the third plant has a benefit of $9 per day. For Greg, the first plant has a benefit of $41 per day, the second has a benefit of $28 per day, and the third has a benefit of $6 per day. For Ray, the first plant has a benefit of $31 per day, the second has a benefit of $19 per day, and the third has a benefit of $2 per day. Given that no one else will see the plants, no one else values the plants in the lobby. 

What is the marginal social benefit of the first plant