hey i would really appreciate it if somebody could answer this:

Assume that product codes are formed from the letters S, W, Q, T, R, and Y, and consist of 4 not necessarily distinct letters arranged one after the other. For example, SSWR is a product code.

(1) How many different product codes are there?

i got this one, it's 6^4 because there are 4 stages and each has 6 options.

(2) How many different product codes do not contain W?

i got this one too, it's 5^4 because instead of 4 stages with 6 options, there are 4 stages with 5 options.

(3) How many different product codes contain exactly one R?

this is the one i haven't been able to get. help please?