There are simple events
and you'll have to write down a few of them to get a feel for what you're looking for in each case.
For three different numbers you do get (6)(5)(4) favorable events.
So you are correct.
In case (b) you can list all the favorable ones, then divide by 216.
HOWEVER, I just reread (c).
That's a conditional, so you will need to be more careful.