Nothing.
No seriously. Artists make nothing from royalties on radio stations, in the US anyways. Only songwriters and publishers do. If the artist happens to also be their own songwriter, then they get about 50% of the royalties. How much the royalties are varies significantly based on the level of pull from the station and of course, how popular the artist is at the time. Their money comes from direct sales of songs, whatever comes from streams, live performances, etc.