permutations and combinations

Please shows steps. thank you for your help.

1. Howmany ways can 7 books be arranged in a shelf if 3 particular books must beseparated? (Ans: 2 880)

2. In howmany ways can we put 4 people in 10 rooms if twoof them must stay in the same room, other in separate room. (Ans: 720)

3. 4boys and 5 girls are to be seated in a row. In how many ways can this be doneif thegirls and boys must be seated alternatively. (Ans: 14 400)

4. 4 booksand 6 magazines are to be arranged in 2 rows of 5 copies each. At least 2 booksmust be on the first row and at least 2 magazines must be on the second row.What is the total number of arrangements? (Ans: 2 678 400)

5. A and B invite 8 friends to a party. The participants are arranged in 2 rows of 5 in order to take photos. Find the number of arrangements if
(a) No restriction (Ans: 725 760)
(b) A and B are next to each other. (Ans: 645 120)

thank you