Let compare the price we have to pay for the 20-pound baggage and the 50-pound baggage. We are going to see that the 50-pound baggage costs $15. From this, we can see that the increase of the weight by 30 pounds resulted in the cost being $15 more. Now in order to find out the rate of change we divide $15 by 30 pounds so we know how much each pound costs, and so we get...
