# Combinatorics: how many ways to organize $4$ books in $7$ different boxes?

I'm trying to figure out this problem in combinatorics and can't seem to find the right approach: If you have $$4$$ books and $$7$$ boxes, where each box can contain several books (or none) - how many possibilities are there to organize said books in the boxes?

I think I should use the binomial equation somehow, but can't figure it out.