At a certain banquet there are 5 options for an appetizer, 7 options for the main course and 6 options for the dessert. How many different full meal options are there? (Note. One full meal differs from another if they differ in at least one aspect: appetizer, main course or dessert.)

I understand how to do this with multiplication, however I don't understand the implementation of P(n, r) and C(n, r). Could you explain this with your answer? Thanks!