How many different arrangements of 5 letters can be formed if the first letter must be $W$ or $K$ (repeats of letters are allowed)? There are different 5 -letter combinations that can be formed. (Simplify your answer.)

Step 1 ：The problem is asking for the number of different arrangements of 5 letters that can be formed if the first letter must be either 'W' or 'K'. Repeats of letters are allowed.

Step 2 ：For the first letter, there are 2 choices: 'W' or 'K'.

Step 3 ：For the remaining 4 letters, there are no restrictions, so each of them can be any of the 26 letters in the alphabet.

Step 4 ：Therefore, the total number of arrangements can be calculated as \(2 * 26^4\).

Step 5 ：Using Python to simplify the expression, we find that \(2 * 26^4 = 913952\).

Step 6 ：So, the total number of different arrangements of 5 letters that can be formed if the first letter must be 'W' or 'K' is \(\boxed{913952}\).