In how many ways can i arrange the 6 letters a, b, c, d, e, f?

If there are no restrictions, there can be; 

6 ways x 6 ways x 6 ways x 6 ways x 6 ways x 6 ways = 6^6 ways for the letters a, b, c, d, e and f to be arranged. 

However, if you want to arrange them so that each letter is used only once; 

6 ways x 5 ways x 4 ways x 3 ways x 2 ways x 1 way = 6! ways 

Hope I helped :) 

The answer is why would a teacher ask that