The slope definitions:
The slope is the change in y divided by the change in x.
The slope is the ratio of rise to run.
The slope is the rate of change of the function at a certain point.
The slope is the first derivative of a function.
The slope is the tangent of the slant/inclined angle
So we are interested in this one: "The slope is the ratio of rise to run"
Logically, the gas in the tank decreases as the distance traveled increases.
So they are inversely proportional.
Let's look at the scale of the axis now///
After examine, as we travel 20 miles, our gas in the tank decrease by 3 gallons...i.e. 3 gallons have been consumed to move this distance
I hope that helps!
I am with you if you faced any difficulties!