The function f is defined by f x = x 3 + 9 . What is

Choice C is correct. It's given that $f\left(x\right)=x^3+9$. Substituting $2$ for $x$ in this equation yields $f\left(2\right)={\left(2\right)}^3+9$. This is equivalent to $f\left(2\right)=8+9$, or $f\left(2\right)=17$.

Choice A is incorrect. This is the value of $2+3+9$, not $2^3+9$.

Choice B is incorrect. This is the value of $2\left(3\right)+9$, not $2^3+9$.

Choice D is incorrect. This is the value of $3^2+9$, not $2^3+9$.