You have a coupon for $40 off any book purchase equal to or greater than $100 (A minimum order of $100 would only cost you $60.). As part of Read Across America Day, amazon. com offers an additional 15% off for book purchases greater than or equal to $100.Use function notation to describe the cost of a book order greater than or equal to $100: With your $40 off coupon alone: f(x) = and With the 15% off discount alone: g(x) =