A) How many one-to-one functions are there from a set with four elements to a set with five elements? (b) How many one-to-one functions are there from a set with four elements to a set with three elements? (c) How many one-to-one functions are there from a set with four elements to a set with four elements? (d) How many one-to-one functions are there from a set with four elements to a set with six elements? (e) How many one-to-one functions are there from a set with m elements to a set with n elements, where m ≤ n?