SAT Question 1863e3be: Nonlinear Functions answer and explanation with Desmos solution

It's given that the y-intercept of the graph of $y=x^2+31$ in the xy-plane is $\left(0,y\right)$. Substituting $0$ for $x$ in the given equation yields $y={\left(0\right)}^2+31$, or $y=31$. Thus, the value of $y$ is $31$.