Question 1104227
let x equal your miles.
let y equal the number of gallons of gas.


it's a linear relationship.
the slope intercept form of a linear equation is y = mx + b
m is the slope
b is the y-intercept.


you have 2 coordinates you can work with.
they are (120,12) and (220,8.66)


let the first one be (x1,y1).
let the second one be (x2,y2).


m = slope = (y2-y1) / (x2-x1) = (8.66-12)) / (220-120) = -.0334
equation of y = mx + b becomes y = -.0334 * x + b


use either one of the points to find the y-intercept.
i'll use (120,12).
replace y with 12 and x with 120 to get 12 = -.0334 * 120 + b
solve for b to get b = 16.008


the equation becomes y = -.0334 * x + 16.008


when x = 0, you have a full tank.
when x = 120, you have -.0334 * 120 + 16.008 = 12
when x = 220, you have -.0334 * 220 + 16.008 = 8.66


to find out when the tank will be empty, set y = 0 to get 0 = -.0334 * x + 16.008.
subtract 16.008 from both sides of this equation to get -16.008 = -.0334 * x.
divide both sides of this equation by .0334 to get -16.008 / .0334 = x.
solve for x to get x = -16.008 / .0334 = 479.2814371.


the tank will be empty after the car has driven 479.2814371 miles.


the equation can be graphed.
the graph looks like this:


<img src = "http://theo.x10hosting.com/2017/120903.jpg" alt="$$$">


since you tank holds 16.008 gallons of gas and you can travel 499.2814371 miles before you run out of gas, then your gas mileage is equal to 479.2814371 / 16.008 = 29.94011976 miles per gallon.


that's approximately equal to 30 miles per gallon based on 16 gallon capacity  and 480 miles range.