3、Xiao Yuchun is reading a storybook. If she reads 15 pages every day, she will finish it in 24 days; if she reads 3 more pages each day, $\qquad$ days will be needed to finish the book.
【Analysis】The book has $15 \times 24=360$ pages. If 3 more pages are read each day, then 18 pages are read each day, and it will take $360 \div 18=20$ days to finish the book.