Essential Genetics 6th Edition by Daniel Hartl

Exercise 6

In a random sequence consisting of equal proportions of all four nucleotides, what is probability that a particular short sequence of nucleotides matches a restriction site for:
(a) A restriction enzyme with a 4-base cleavage site?
(b) A restriction enzyme with a 6-base cleavage site?
(c) A restriction enzyme with an 8-base cleavage site?