Given:
[tex]y+3x^2=4[/tex]We have that y f(x), so solve for f(x):
[tex]\begin{gathered} y+3x^2-3x^2=4-3x^2 \\ y=4-3x^2 \\ f(x)=4-3x^2 \end{gathered}[/tex]And for f(4):
[tex]f(4)=4-3(4)^2=4-3(16)=4-48=-44[/tex]Answer:
[tex]\begin{gathered} f(x)=4-3x^{2} \\ f(4)=-44 \end{gathered}[/tex]