Hello! Does anybody know the OST, that had been played at the end of episode 4? 

I searched for it everywhere, but I couldn't find it. :)

The one that is sung by a lady with a husky voice, I am also wondering!!! 

 MarazulOx:

The one that is sung by a lady with a husky voice, I am also wondering!!! 

Yes that one! I don't think it is out yet. :(

Thank  you so much!!! and the singer is Lee Youngji, not to be confused with another Youngji that was in a Kpop girl band.  

 MarazulOx:

Thank  you so much!!! and the singer is Lee Youngji, not to be confused with another Youngji that was in a Kpop girl band.  

No, the rapper is Lee Yong Ji.  She's only 20 or 21 and has already won awards.  She's been rapping professionally since she was in high school.  I like her.   Although her image is changing, she'd never be confused as an idol for a girl group.

https://www.youtube.com/watch?v=mjwVZeLVz44