This may not be correct but if there is 5 letters(abcde) then there is with each letter a possibilty of 5 different sets with a cobination of 3 letters. for example aaa,aab,aac,aad,aae,the switch the last letter to the middle for each letter aba,aca,ada,aea, etc. this leads to there being 5 for each letter using only a and since there is 5 letters you multily 5 by 5 for the different sets then by another 5 or 5^3. so 125 if u still need the answer.