Which one is correct?

Dan mcclure is trying to decide on how many copies of a book to purchase at the start of the upcoming selling season for his bookstore. the book retails at $28.00. the publisher sells the book to dan for $20.00. dan will dispose of all the unsold copies of the book at 75 percent off the retail price, at the end of the season. dan estimates that demand for this book during the season is normal with a mean of 100 and a standard deviation of 42. a. how many books should dan order to maximize his expected profit? b. given the order quantity in part a, what is dan's expected profit? c. the publisher's variable cost per book is $7.50. given the order quantity in part a, what is the publisher's expected profit?