If you read a book with 80 pages a day, you can’t finish it in 4 days, but you have more than 5 days; if you read 90 pages a day, you can’t finish it in 3 days, and you have more than 4 days; Natural number) After reading in days, how many pages is this book.
一本书如果每天读80页，那么4天读不完，5天又有余；如果每天读90页，那么3天读不完，4天又有余；如果每天读N页，恰好N(N是自然数)天读完，这本书是多少页．
<gadget id="calculator">18 * 18</gadget>
<output>324</output>

<result>324</result>