Verified Answer :

naǫ

\(f(x)=8-3x^2 \hbox{ when } x=3 \\ \Downarrow \\ f(3)=8-3 \times 3^2=8-3 \times 9=8-27=\boxed{-19}\)

The answer is -19.

F(x)=8-3x2
f(3)=8-3(3)2
8-27=-19