Compute the slope with $m=\dfrac{\Delta y}{\Delta x}$ using the coordinates of $P$ and $Q$.

If one point has $x=0$, its $y$-value is the intercept $b$ in $y=mx+b$.

In Desmos, compute m=(4-12)/(40-0).

Since point $P$ is $(0,12)$, set b=12 and enter y=m x + b.

Compare the equation you entered with the answer choices and select the matching one.

From the graph, the labeled points on the line of best fit are $P(0,12)$ and $Q(40,4)$. (Here $x$ is in thousands of miles and $y$ is in millimeters.)

Since point $P$ is at $x=0$, the line’s $y$-intercept is $b=12$. Therefore the line of best fit is