How do I approach her?

I am working in a company and a month back there is a girl joined that company in starting i was not talking with her just busy in my work and other things but once a day when i was leaving the company in evening she came in lift and we walked together and from that day I don’t know what happened but i started attracting towards her she seems a very nice girl and it feels she is same like me in thinking and in some other things. Now i am going with her everyday after finishing work but i am very introvert guy I don’t talk much always stays silent and just 2-3 days ago i started talking with her on whatsapp just normal talking but it feels good and she reply too whenever she come online but i feel scared to send her message, I don’t know what she will think if i send her message. And I don’t know she is already committed or not. Lots of things happening in mind. Can someone please tell how to approach her and ask her for a date and if she got boyfriend already what to do in that situation. After talking with her I realised she is very nice and special and her smile is so beautiful in goggles. Please give some suggestions what should i do for next step?
How do I approach her?
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