L Homework Question 39, 10.3.47 HW Score: $95.38 \%, 62$ of 65 points Points: 0 of 1 Save Television and radio stations use four call letters starting with W or K, such as WXYZ or KRLD. Assuming no repetitions in the second to fourth letters, how many four-letter sets are possible using either $W$ or $K$ and only the letters $F$ to $X$ ? (Count all possibilities even though, practically, some may be inappropriate.) There are four-letter sets that can be formed.

Step 1 ：There are four-letter sets that can be formed.

Step 2 ：The first letter can be either W or K, so there are 2 choices for the first letter.

Step 3 ：The second to fourth letters can be any of the letters from F to X, inclusive. There are 19 such letters (X - F + 1 = 24 - 6 + 1 = 19).

Step 4 ：Since no repetitions are allowed in the second to fourth letters, we have 19 choices for the second letter, 18 choices for the third letter, and 17 choices for the fourth letter.

Step 5 ：Therefore, the total number of four-letter sets is the product of these choices, which is \(2 \times 19 \times 18 \times 17 = 11628\).

Step 6 ：Final Answer: There are \(\boxed{11628}\) four-letter sets that can be formed.