The table shows the changes in the cost to mail a letter in the United States since 2000. What is the average rate change of cost with

Since functions represent how an output quantity varies with an input quantity, it is natural to ask about the rate at which the values of the function are changing.

For example, the function C(t) below gives the average cost, in dollars, of a gallon of gasoline t years after 2000.

The graph isn’t that clear