SAT Question c81f1c2f: Linear Functions answer and explanation with Desmos solution

It’s given that the function $f\left(x\right)=45x+600$ gives the monthly fee, in dollars, a facility charges to keep $x$ crates in storage. Substituting $50$ for $x$ in this function yields $f\left(50\right)=45\left(50\right)+600$, or $f\left(50\right)=2,850$. Therefore, the monthly fee, in dollars, the facility charges to keep $50$ crates in storage is $2,850$.