In a bookcase, all books are sorted by whether they are fiction or non-fiction
and whether they are paperback or hardback.
The ratio of fiction books to non-fiction books is 6: 1.
The ratio of paperback fiction books to hardback fiction books is 4:11.
The ratio of paperback non-fiction books to hardback non-fiction books is
2:3.
Work out what fraction of the books are hardback.
Give your answer in its simplest form.