Hey hey. I'm really struggling with this part of Complex analysis.

Q. Which of these sets are open? closed? Justify your answer.

(a) { z : Im(z) > 0 } ; (b) { z : Re(z) > 0, lzl<2 } ; (c) { z : lzl^2 <= 6 }

I have to use the definition of open and closed sets to answer these 3 questions. I'm aware of the definitions, but don't really know how to apply them to problems. Any help would be appreciated. Thanks in advance.