[填空题]
Julie works at a book store and hkar++4;* j ted)gagq yas nine books to disjbrb9x ,mm7z ,play 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 ca,xrjmb b7,9 mzn 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.
