The fuel (y) Karl has in his car is a function of the distance (x) Karl travelled. The amount of fuel (y) is dependent on the distance (x) Karl travelled.
On the y-axis, we have amount of fuel.
On the x-axis, we have distance travelled.
At the time Karl travelled when he had 200 liters of fuel (y) remaining in his car, he had travelled a distance (x) of 500 kilometers.
We know this by looking at the graph given. When x (distance) = 500, y (fuel) = 200.
