I will start off with that I am young only 19 so I realize I lack experience

Had to get some groceries as I walked by a till on my way down one of the aisles i notcied a major cutie cashier we made eye contact she smiled and I went on with my shopping.

Once I was done of course I picked her checkout but there was only 2 anyway.

I wait for her to ring the other guy through check her out somewhat lol. She tries to scan this free axe travel bag and I tell her it said take 1. She says oh okay. I question her: Your not going to check to make sure. Tells me shes too lazy so I tease her about that and how I could be making off with a free item and she will have to go to jail for me.

She forgot to ask how many bags i needed ) ihad like 4 items) but for fun i said well with the amount of stuff i have here 100 shall do smirk on my face...she grins then i say nahh just 1 and she laughs. Bring up about how she never said hi and are you always that rude with your customers.

Anyway thats me rambling since the bottom line is how can I get a number close out of that or any interaction with a cashier or a girl working for that matter?
How long do I need to talk and build attraction plus comfort?