How do I approach this girl?

So I went to school with this girl 6 years ago. Stupid schoolboy stuff, was my 'gf' although nothing happened. Now it's 6 years later after the occasional 'Happy birthday' we had a conversation through Facebook and I have feeling for her again.
All I know is that we live near eachother, how do I find if she is single, likes me and how do I go about asking her out?
How do I approach this girl?
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