what background songs , in eps 12 scene eun gi and da in drunk??please answer...

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That lounge piano song I've no clue but the latter one with the whistling is:
U, Who by Inhee Choi, Hyunil Seo & Jijyoung Min

You can find the whole album including the instrumental/composed songs like this one on Spotify. I have quite a few songs in my OST playlist(k-scores you can find the link in my bio) from that album.
Just type "Her Private Life(Original Television Soundtrack)" and you'll be able to find the full album.