As you can see, both variables are directly proportional.
Thus, the given line should have the form:
[tex]y=kx[/tex]
Where k is the proportionality constant.
To find the number of gallons of gas needed to drive 120 miles, we should find k first.
Notice that we need 1 gallon of gas to drive 25 miles and 2 gallons of gas to drive 50 miles. The rate of change (k) between these variables is:
[tex]\frac{50-25}{2-1}=25\frac{gallons}{\text{mile}}[/tex]
This means that it takes 25 gallons to drive each mile.
Now, we could replace:
[tex]\begin{gathered} 120=25x \\ x=\frac{120}{25}=4.8\text{gallons} \end{gathered}[/tex]
Therefore, Justin needs 4.8 gallons to drive 120 miles.
