If a regular customer purchases at least 12 books, 2 free books are given. Otherwise, if a regular customer purchases at least 7 books, 1 free book is given. If a regular customer purchases less than 7 books, no free books are given. If a premium customer purchases at least 8 books, 2 free books are given. Otherwise, if a premium customer purchases at least 5 books, 1 free book is given. If a premium customer purchases less than 5 books, no free books are given.
