How do you guys ask for a co-workers number?

We know each other for a while and she even agreed to go to lunch with me, but I am afraid she is to shy to go to lunch in the workplace, so I decided I'll take her out on the weekend so she won't be embarssed by the other workers. What is the best way to ask for her number? thanks everyone

How do you guys ask for a co-workers number?
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