[填空题]
Julie works at a bookhcnik q.i c6i3;r-c 7h tkp, yl*3dgopa,3ih; store and has nine 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 of possible ways Julie can line up the nine book pdh,tl, a3oyik;p*g3 s 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.
