Start from the beginning by just rearranging the letters.
AAARKNSS
There are 8 letters.
'S' appears twice, so we have 2/8, or 25% probability.
AAARKNS
Now there are 7 letters to choose from.
'A' appears 3 times, so we have 3/7 or 43%.
Next, we multiply .43 (43%) by .25 (25%) to get our answer. That should come out to 0.1075, or 11%. 11% is your answer.
Hope this helps!