Hey QM....this is VERY similar to your other question which I showed you how to answer....you should be able to do this one....try it!
https://web2.0calc.com/questions/help-ep
This is very easy...
We have $f(3) = 12(3)^9 + 3$ and $f(-3) = 12(-3)^9 + (-3)$. Adding, this is $12(3)^9 + 3 + 12(-3)^9 + (-3)$. Since $(-1)^9 = -1$, this simplifies as $12(3)^9 + 3 - 12(3)^9 - 3 = \boxed{0}$.