They will both be replaced the 18th month.
Though you did not list the points, I can tell you how to solve for the question.
One way to tell if a point lies on a given line is to take the point and plug it into the equation. If the equation remains true, then the point lies on the line. For example:
If we have the point (1,1), we can plug in 1 for x and 1 for y and see if the equation is true:
What are the choices ? ? It's about 69 miles or 111 km.
