Xiaohong reads a book, and the number of pages she has read is 15 of the whole book, and she reads another 51 pages. At this time, the ratio of the number of pages read to the number of unread pages is 1:3. How many pages does this book have.
小红读一本书，已读页数是全书的15，她又读51十页，这时已读页数和未读页数的比是1：3．这本书共有多少页．
<result>240</result>