Give the step-by-step reasoning process and then the final answer. Candice read 3 times as many books as Amanda in their school's Book Tournament. Kara read half the number of books that Amanda read, and Patricia read 7 times the number of books that Kara read. If Candice read 18 books, how many books did Patricia read?

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.
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Amanda read 18 / 3 = 6 books. Kara read 6 / 2 = 3 books. Patricia read 7 x 3 = 21 books.
The final answer: 21.