Hi, I'm really in a pinch. Can anyone help me understand this?

Assume sets A and B are non-empty and unequal

a)B-A=Null

b) A U B = B

c) A-B = A

I hope someone can help me through venn diagrams, easier to understand. I searched for hours in the internet..either I suck at searching or there's just nothing...

I appreciate any smart person who'd be able to help me with this..

thanks..