The steepness of the line on which the plane is descending is 1/3Explanation:The steepness of a lines tells us how steep this straight line is. In other words, this is the slope of the line. This can be calculated as:[tex]steepness=\frac{Change \ in \ y}{Change \ in \ x}=m[/tex]From the figure, the plane is descending through a line whose Change in y and x are as follows:[tex]Change \ in \ y:1000ft \\ \\ Change \ in \ x:3000ft[/tex]So:[tex]steepness=\frac{1000}{3000}=\frac{1}{3}[/tex]So the steepness of the line on which the plane is descending is 1/3Learn more:Inverse variation: