Bro
1) YouTube Views on an avg u earn 5$ from 1000 views...So Radha has earned around 150,000 USD approx 100,000 USD from other songs..So 250,000 USD till now from YouTube only..Bound to increase much more
2) Saavn/Gaana/I tunes
3) On TV on music channels like 9xm
4) Sell them on Radios..
5) Old school people who buy CD's and cassettes