At the beginning of a semester, Dirk is willing to pay $180 for a textbook, but gets it for$140 at the university bookstore. When he has completed the course, the book is worth only $40 to him. He can keep it or sell it back to the bookstore. The bookstore will pay him 35% of the original price. If Dirk makes his best choice, overall, he will (gain or lose) a value of$_.