SAT Question de362c2f: Nonlinear Functions answer and explanation with Desmos solution

Choice D is correct. It's given that the function $f$ is defined by $f\left(x\right)=5x^2$. Substituting $8$ for $x$ in $f\left(x\right)=5x^2$ yields $f\left(8\right)=5{\left(8\right)}^2$, which is equivalent to $f\left(8\right)=5\left(64\right)$, or $f\left(8\right)=320$. Therefore, the value of $f\left(8\right)$ is $320$.