How many rakkah shuld we pray for taraweeh?

i went first time today alhamdulilaah, and i did 20 (may Allah subhanhu wa ta'ala except from me), sum left after 8 and sum left after 12, i was told there was difference of opinions between each 3, so what is ryt, backed with Quran and/or sunnah please... hukren and salaam