How many different 4-letter radio-station call letters can be made if the first letter must be k or w, repeats are allowed, but the call letters cannot end in an o?

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We have four slots to fill.
The first slot can only be one of two choices, so the first slot will have 2 choices.
The second, and third slots don't matter, so there'll be 26 each.
The last slot cannot end in an o, thus there'll be 25 available to choose.

Thus, we get: 2*26*26*25 = 33 800 different ways.