Radio stations use three or four letters for their call letters(name). The first letter must be a W or K. How many different call letters are possible if repeated letters are allowed? And not allowed?

Answer 1

3-letter permutations:
= 2x26x26 = 1352
4-letter permutations:
= 2x26x26x26 = 35152
total = 36504

If not repetition allowed
3-calls = 2x25x24 =
4 letters = 2x25x24x23 =
total = ..

Answer 2

Fille in the blank
1,3,5,7,9,11,13,15