SAT Question d0a7871e: Nonlinear Equations In One Variable And Systems Of Equations In Two Variables answer and explanation with Desmos solution

Choice A is correct. It is given that $y=x+1$ and $y=x^2+x$. Setting the values for $y$ equal to each other yields $x+1=x^2+x$. Subtracting $x$ from each side of this equation yields $x^2=1$. Therefore, $x$ can equal $1$ or $-1$. Of these, only $-1$ is given as a choice.