The local council is considering providing public access to camping grounds for free for a couple of days per month, loulia, Alex and Cid are the only potential users of the campgrounds. Their willingness to pay for the good are as follows: Ploulia - 10-Q; PAlex 30-3Q; and Pcid-20-2Q, where Q is the number of days they would be staying in the campground. There are no fixed costs, and the marginal cost of providing the good is given by MC - 20+20 The optimal number of days to make campground available is