I presume you know the answers (as you know that one is wrong) so I'll give you what I got:
How I got them? Well, I started by looking at the unions of the sets:
, etc. Then, I couldn't think up some clever way so I decided to do the obvious thing and...draw a diagram!
Draw three circles which all intersect one another. Label them A, B and C. There should be a triangle in the middle where they all intersect one another - this represents the set . Similarly, where the circles A and B intersect this represents the intersection of the sets A and B, etc. We shall now put numbers in the spaces to represent the size of the sets.
So you know what to put in - that's a 4. What about in - that's simply 22-4=18. Then just continue putting numbers into this diagram until every space has a number in it. Questions 1 and 2 are easily read from this diagram, and question 3 isn't really hard to see on the diagram either...
I hope that makes sense, and also that it helps!
EDIT: essentially, the answer to part 1 is the cardinality of the set , which is as you have "removed" twice (as it is in both and ) so you need to put one of them back.
EDIT 2: Your diagram should look something like
just with different numbers, and less stolen from someone else's web site...(it's too big to put in my post properly)