First you find out how much each backpack weighs. For the singular unit you do 27/3 which equals 9. Then it says he gives someone 2 of his books and puts 3 in his locker. That means 5 books are coming out of the bag. 9-5 would equal 4. Then you would times each of the books by 3. That would be 4x3 to get 12.
