If there were 5 different letters, there would be 5! ways of arranging them.
However, since there were two copies of the letter X, we need to divide that answer by 2!.
And, since there were two copies of the letter E, we need to divide that answer by 2!.
5! / 2! / 2! = 120 / 2 / 2 = 30 different arrangements of the letters.