Question

How many different 4-letter radio station call letters can be made if repeats are allowed and the first letter must be k?

Answer 1

The first letter has to be a k, so the first letter only has one option.
The second letter can be any letter, so there are 26 options. This is the same for the third and fourth letter as well.
To find all possible options, you must multiply all of these "options" together.
1•26•26•26=17576