SAT Question fcb78856: Nonlinear Equations In One Variable And Systems Of Equations In Two Variables answer and explanation with Desmos solution

Choice A is correct. It's given that the equation $b=42cf$ relates the positive numbers $b$, $c$, and $f$. Dividing each side of the given equation by $42f$ yields $\frac{b}{42f}=c$, or $c=\frac{b}{42f}$. Thus, the equation $c=\frac{b}{42f}$ correctly expresses $c$ in terms of $b$ and $f$.