Answer:
The domain is

The range is:

Explanation:
Domain and range of a function:
The domain of a function are the values that the input assumes, while the range are the values that the output assumes.
In this question:

m is the input, which is the number of phone calls, which can be any number between 0 and infinite. So
The domain is

When the input is m = 0, the value of C(0) = 20. As m increases, so does C(m). This means that:
The range is:
