SAT Question 3e28a622: Nonlinear Functions answer and explanation with Desmos solution

Choice C is correct. It's given that function $g$ is defined by $g(x)=\sqrt{x}+300$. Substituting $81$ for $x$ in function $g$ yields $g(81)=\sqrt{81}+300$, which is equivalent to $g(81)=9+300$, or $g(81)=309$. Therefore, the value of $g(x)$ when $x=81$ is $309$.