A. AHSNKUV Words are arranged in ascending order. Thus if you take last five letters you get 5! = 120 combinations so our first ywo letters are AH . Now when you arrange last five letters in ascending order you get KNSUV .
So Place K at position 3 you get 4! = 24 combinations
then Place N at position 3 you get 4! = 24 combinations
Then Place S at position 3 and K at position 4 you get 3!= 6 combinations
Total = 54 combinations
55th AHSNKUV