Your answer would be x-4=17.
4 less than (#) is 17.
That number would be 21.
21-4=17
Hope that helps
If

then

Differentiating with respec to
gives


So
is indeed conservative, and

Because if you know where the line crosses the y axis (the y intercept) you can plot a point there. Then with slope you can count to your next plotted point. With the 2 points you can now draw your line.