[填空题]
Julie works at a book store ands(8wnd3gio9-jxc1j ly vh8e nk;- 2 bu has nir6lyh q3j12n dne books to display on the main shelf of the store. Four of the books are non-fiction and five are fiction. Each book is different. Determine the number o hjn3q2lyrd1 6f possible ways Julie can line up the nine books on the main shelf, given that
1. the non-fiction books should stand together;
2. the non-fiction books should stand together on either end;
3. the non-fiction books should stand together and do not stand on either end.
