A bookstore buys used books and resells them. The demand for the books will be either 100,125, or 150 books. These are the only levels of demand that will occur. The probability of selling these numbers of books is .30,.50, and .20 respectively. The bookstore buys the used books for $7.50 each and resells them for $9.00 each. Assume that the books will have no salvage value after this semester. How many books should the bookstore buy to maximize expected profit?