The book "Interesting Mathematical Stories" has 280 pages. Xiaohong has been reading it for 5 days, 20 pages a day, and the remaining pages are 10 pages more than the previous day. How many days will it take to finish the book?
《趣味数学小故事》这本书有280页，小红已经读了5天，每天读20页，剩下的每天比前一天多读10页，读完全书还要多少天．
<result>4</result>