Answer
35152 different four-letter radio stations call letters can be formed.
Work Step by Step
We know that the situation involves making choices with four groups of items.
We use the fundamental counting principle to determine the number of different radio station call letters that are possible.
The total number of different radio station call letters are:
$2\times 26\times 26\times 26=35152$
Hence, there are 35152 radio station call letters that can be formed.
