SAT Question 0b0fa68b: Linear Functions answer and explanation with Desmos solution

It's given that $f(cx)=x-8$ for all values of $x$, where $c$ is a positive constant, and $f(2)=35$. Therefore, for the given function $f$, $cx=2$. Dividing both sides of this equation by $c$ yields $x=\frac{2}{c}$. Substituting $\frac{2}{c}$ for $x$ in the equation $f(cx)=x-8$ yields $f(\frac{2c}{c})=\frac{2}{c}-8$, or $f(2)=\frac{2}{c}-8$. Since it’s given that $f(2)=35$, substituting $35$ for $f(2)$ yields $35=\frac{2}{c}-8$. Adding $8$ to both sides of this equation yields $43=\frac{2}{c}$. Multiplying both sides of this equation by $c$ yields $43c=2$. Dividing both sides of this equation by $43$ yields $c=\frac{2}{43}$. Note that 2/43, .0465, 0.046, and 0.047 are examples of ways to enter a correct answer.