SAT Question 447fa970: Linear Functions answer and explanation with Desmos solution

The value of $f\left(x\right)$ when $x=4$ can be found by substituting $4$ for $x$ in the given equation $f\left(x\right)=7x+2$. This yields $f\left(4\right)=7\left(4\right)+2$, or $f\left(4\right)=30$. Therefore, when $x=4$, the value of $f\left(x\right)$ is $30$.