To understand Ron-Jon's equation, let's recall the slope-intercept form. We can see that Ron-Jon's equation is in slope-intercept form. Now, let's write our own equation of the problem and compare it with Ron-Jon's. We are told that Lena-Jon starts counting the days left when it's days left. Thus, the -intercept can be interpret as Since the days left decrease by one each day, the slope should be Thus, this gives us the equation Hence, Ron-Jon mixed up the slope and -intercept.