. . "But still it could be good for practice.We have 8 letters from which 6 are unique.Possible scenarios for 4 letter selection are:A. All letters are different;B. 2 N-s and other letters are different;C. 2 E-s and other letters are different;D. 2 N-s, 2 E-s.Let's count them separately:A. All letters are different, means that basically we are choosing 4 letters form 6 distinct letters: 6C4=15;B. 2 N-s" . .