Let's pretend you're traveling 100 miles, this will cost $180.13. If you
want to travel 101 miles, this will cost you $180.33. The difference here is 20
cents and notice that's the slope. Remember when we said earlier that the slope
is the change in y, after we change x by one unit. In this case the units are
miles. So with every additional mile traveled, you would expect to pay 20 more
cents.