How many different arrangements of 7 letters can be formed if the first letter must be w or k? (repeats of letters are? allowed)?

The total number of different arrangements of 7 letters that are possible if the first letter will be w or k is:

                        617,831,552

The number of different arrangements of 7 letters can be formed if the first letter must be w or k such that the repetition of the letters are allowed are:

   2×26×26×26×26×26×26

( Since, at the first place any of the 2 letter out of w or k could come up.

and from the second to seventh place any of the 26 letters of the English alphabet may come up )

Hence, total number of arrangements = 617,831,552