f(-3)=2(-3)^3+4(-3)^2

$2\times{(-3)}^{3}+4\times{(-3)}^{2}$

$2\times-27+4\times{(-3)}^{2}$

$2\times-27+4\times9$

$-54+4\times9$

$-54+36$

$-18$

Assuming you are trying to simplify it, you first do the exponents in each piece, so -3^3 and -3^2, and you take those answers and multiply them by their respective numbers outside the parenthesis. I believe if done correctly your final answer should be -18.

-18