{3000-[300+30*(30-14)]}*4=8880
that means, if your Tige 30, Gengu 30, then you have to get at least 8880 neili(88nian neili) to get 3000 qx.
but normally, no people will choose both tige and gengu to be 30.
let's calculate another option with the average of Gengu and Tige is 25.
{3000-[250+25*(30-14)]}*4=9400
94nian neili....addoil........*hoho