Button to open form as pop up

I'm trying to complete this button so it will take the record ID in as a variable.   (The team have asked for this as a pop up, I this can be opened as a new tab).  

Hardcoded it does what I'm asking it to do.

"<a class='Vibrant Success' onclick=\"var a=window.open('https://xxxxxxxx.quickbase.com/db/xxxxxxxx?act=API_GenAddRecordForm&_fid_39=17074', 'newwindow', 'width=1200,height=600');\" >Add Contact 2</a>"

But as I want to pass [Record ID#] and this is where I get stuck.

I'm not sure how to add '=API_GenAddRecordForm&_fid_39= & ([Record ID#])'

Any help appreciated.