How many 3-letter combinations are possible from the first seven letters of the alphabet?

Answer 1

Permutations of 7 items taken 3 at a time.
The order matters so it is permutations, not combinations.
Look at "ordered subsets" in the link:
http://dwb4.unl.edu/Chem/CHEM869N/CHEM869NMats/Permutations.html

7! / (7-3)! = 7!/4! = 7*6*5 = 210