[填空题]
Julie works at a book store and has nine books to displ.iqt2 jz7 0igmay on the main shep ine4 )wy zyq6ggp-5(lf of the store. Four of the books are non-fpi 4yp-w56qg(n )gyeziction and five are fiction. Each book is different. Determine the number of 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.
