There are 6 math books, 4 chemistry books, and 6 physics books.
to. In how many ways can they be placed on a shelf horizontally, if the books for each subject must go together?
b. How many ways can they be placed on a shelf horizontally, if only math books need to go together?
c. How many ways can they be placed on a shelf horizontally, if only chemistry and physics should go together and can be mixed together?
d. In how many different ways can we choose 3 math books, 2 chemistry books, and 2 physics books to donate to a library?