SAT Question ff2c1431: Nonlinear Equations In One Variable And Systems Of Equations In Two Variables answer and explanation with Desmos solution

Choice B is correct. It's given that the equation $7m=5\left(n+p\right)$ relates the positive numbers $m$, $n$, and $p$. Dividing both sides of the given equation by $5$ yields $\frac{7m}{5}=n+p$. Subtracting $p$ from both sides of this equation yields $\frac{7m}{5}-p=n$, or $n=\frac{7m}{5}-p$. It follows that the equation $n=\frac{7m}{5}-p$ correctly gives $n$ in terms of $m$ and $p$.