SAT Question b8fa27db: Linear Equations In Two Variables answer and explanation with Desmos solution

It's given that line $k$ is parallel to line $j$. It follows that the slope of line $k$ is equal to the slope of line $j$. Given two points on a line in the xy-plane, $\left(x_1,y_1\right)$ and $\left(x_2,y_2\right)$, the slope of the line can be calculated as $\frac{y_2-y_1}{x_2-x_1}$. In the xy-plane shown, the points $\left(0,5\right)$ and $\left(1,9\right)$ are on line $j$. It follows that the slope of line $j$ is $\frac{9-5}{1-0}$, or $4$. Since the slope of line $j$ is equal to the slope of line $k$, the slope of line $k$ is also $4$.