SAT Question 40f2e601: Nonlinear Equations In One Variable And Systems Of Equations In Two Variables answer and explanation with Desmos solution

Choice D is correct. It's given that the values of $P$, $N$, and $C$ are positive. Therefore, dividing each side of the given equation by $N$ yields $\frac{P}{N}=19-C$. Subtracting $19$ from each side of this equation yields $\frac{P}{N}-19=-C$. Dividing each side of this equation by $-1$ yields $19-\frac{P}{N}=C$, or $C=19-\frac{P}{N}$.