There are 30 books to be placed inside a 3 shelf cupboard. If the shelves hold a maximum of 10 books, calculate the number of arrangements of the books. Using combinations and permutations.

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?