Solution for 1a in line 2.
For 1b think a little!
I don't see the point of that using the inclusion-exclusion theorm...arg...this is the annoying thing about not having the solutions...don't know how they want us to do it...
Thankyou for your reply Plato
EDIT: WAIT NEVER MIND I GET IT NOW!! Silly me was thinking it was the actual numbers, rather than how many were in the set!