Give the step-by-step reasoning process and then the final answer. Sally reads 10 pages of a book on weekdays and 20 pages on weekends. If it takes 2 weeks for Sally to finish her book, how many pages that book has?
Two weeks has 5 * 2 = 10 weekdays. Two weeks has 2 * 2 = 4 weekends. On weekdays, she reads 10 * 10 = 100 pages in total. On weekends, she reads 20 * 4 = 80 pages in total. So the book has 100 + 80 = 180 pages.
The final answer: 180.