Campus Bookstore Is the Only Textbook Supplier in the Town,a

Campus Bookstore is the only textbook supplier in the town,a profit-maximizing business.The table below represents the reservation prices for the eight students enrolled in the class for which this book is required. $$\begin{array} { c c } \text { Customer } & \begin{array} { c } \text { Reservation Price } \\\text { (\$/book) }\end{array} \\\mathrm { Q } & 60 \\\mathrm { R } & 54 \\\mathrm {~S} & 48 \\\mathrm {~T} & 42 \\\mathrm { U } & 36 \\\mathrm {~V} & 30 \\\mathrm {~W} & 24 \\\mathrm { X } & 18\end{array}$$
Assume that the marginal and average total cost for each book is $12.
Refer to the information above.If the bookstore is selling the socially efficient number of books,how many will it sell?

A) 8
B) 5
C) 6
D) 7