How many 10 long combinations can you make from the repeating set A = {a,b,c,d,e,f,g}

I was supposed to express this in factorials.

What confuses me is the fact that its a repeating set and how this affects the solution. I'm guessing that it would mean that 10 long combinations would look something like this: abcdefgabc,bcdefgabcd, cdefgabcde which would mean that the answer would be ? since we always get 3 letters that goes in twice the combination.