*21. A DNA nucleotide has any of four values. A standard model for a mutational change of the nucleotide at a specific location is a Markov chain model that supposes that in going from period to period the nucleotide does not change with probabilityI mage, and if it does change then it is equally likely to change to any of the other three values, for some .

(a) Show that Image.

(b) What is the long-run proportion of time the chain is in each state?