Answer
An equation relating G to D is:
[tex]G=\frac{-D}{20}+16[/tex]
The graph of the equation is:
Explanation
Note: The general formula for a linear equation is y = mx + c
Now, using the model of a linear equation, we have:
[tex]G=Dm+c[/tex]
'c' is the y-intercept of the equation, (i.e the initial value of G, when D = 0).
So if Keith starts the trip with 16 gallons of gas in his car, we have c = 16.
'm' is the slope of the line, (i.e an increase of 1 in the value of D causes an increase of 'm' in the value of G).
So if the car uses one gallon every 20 miles, the value of m is -1/20 (an increase of 20 in D causes a decrease of 1 in G).
Hence, an equation relating G to D is:
[tex]G=\frac{-D}{20}+16[/tex]
The graph of the equation using a graphing tool is:
