If you read 40 pages of a book every day, you can’t finish it in 8 days, and you have more than 9 days; if you read 50 pages a day, you can’t finish it in 7 days, and you have more than 8 days; Read it in 9 days. How many pages does this book have.
一本书如果每天读40页，8天读不完，9天又有余；如果每天读50页，7天读不完，8天又有余；如果每天读n(n是自然数)页，恰好用9天读完．这本书共有多少页．
<result>351</result>