Answer:
f(x) = 400|x -3|
Explanation:
You want an equation and graph for your distance from mile-marker 12. You are running 400 ft/minute, and are currently 1200 ft from mile-marker 12.
Equation
You will be at mile-marker 12 after an elapsed time of ...
time = distance/speed
time = (1200 ft)/(400 ft/min) = 3 min
At that point, your distance from the marker will be zero.
Your rate of change of distance is 400 ft/min, so the equation might be written as ...
f(x) = 400|x -3| . . . . . distance from marker 12 after x minutes
The graph will have a y-intercept of 1200 ft, and a x-intercept of 3 minutes. The lower right graph looks like that.