SAT Question 4e97f862: Linear Functions answer and explanation with Desmos solution

Choice B is correct. It's given that the function $f$ is defined by $f\left(x\right)=3x-8$. The value of $f\left(7\right)$ is the value of $f\left(x\right)$ when $x=7$. Substituting $7$ for $x$ in the given equation yields $f\left(7\right)=3\left(7\right)-8$, which is equivalent to $f\left(7\right)=21-8$, or $f\left(7\right)=13$.