The question is

A sequence is palindromic if it is unaltereld when read in reverse order. How many palindromic sequences of length 6 are there in the 4 letter code T, A, G, C?

I know the answer is 64, Just not sure how to do it.

(6-4)^6 gives me the right answer, but it just doesn't seem to be right. Any help would be greatly appreciated. Thanks.