Answer: 1,368 books
Step-by-step explanation: To find the total number of science fiction books in the bookstore, you need to multiply the number of bookcases by the number of books in each bookcase. In this case, there are 19 bookcases, each containing 72 books:
19 bookcases × 72 books per bookcase = 1,368 books
So, there are 1,368 science fiction books in the bookstore.