To buy a book, you pay $20 for each of the first 5 books at the supermarket, and for each additional book you buy over $20, you receive a discount of $2. If Beatrice bought 20 books, how much did she pay at the supermarket? Give me reasons, before answering the question

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
For the first five books, the total cost is $20 * 5 = $100. For every additional book over $5, you pay $2 less, totaling to $20 - $2 = $18. Beatrice bought 20 books, so the number of books at which she received the $2 discount is 20 - 5 = 15 books. For the 15 books, Beatrice paid 15 * $18 = $270. In total, Beatrice paid $100 + $270 = $370 for the 20 books. So the final answer is 370.