How many hours a week do I need to work to live on my own but remain a full time student?

I'm trying to figure out how much I would need to work to live on my own and maintain my grades as a full time student. I've looked at rent rates where I live and it looks like it's gonna be about 400 a month, water and electricity and sewer included. I'm a waitress so I make decent money. Any advice would be appreciated!