a)

There are 12 people and we want to pick 4 of them. So, we use

\(\binom{12}{4} = 495\)

b)

First, we know that Mark has to be on the committee, so we put him in immediately. This leaves 3 spots to be filled by 11 people. Hence we use

\(\binom{11}{3} = 165\)

c)

We know that mark cannot be included, so there are 11 people who can go in 4 spots.

\(\binom{11}{4} = 330\)

I hope these are correct!