Probability and Subsets

How many of the three element subsets of the set H={a,b,c,d,e,f} include the letter e ?
Please help me with this.I have the final exam tomorrow.

Thank you in advance

6C3 possibilities without repetition = 20

with the letter e and two other letters will be 5C2 = 10

Let H* be {a, b, c, d, f} and H = H* unite {e}. Then the problem turns into if how many two element subsets H* has got, - and |H*| = 5 - which happens to be C (5, 2) = 10.