Chapter 1 - Section 1.2 - Functions and Models - Exercises - Page 77: 70

The cost of downloading a movie in January is 4 dollars, in February it is 3.81 dollars and in March, it is 3.59 dollars.

The cost of downloading a movie in January is 4 dollars, in February it is 3.81 dollars and in March, it is 3.59 dollars. Here, we can see, that the function of $C(t)=4-0.2t$ is not perfect, but it fits almost perfectly on to the values.