Using the mean concept, it is found that the mean difference between the call times and the company's average call time is given by:
In this problem:
Hence, the mean difference is:
[tex]M = \frac{-2.32 - 1.55 + 4.79 + 0.68}{4} = 0.4[/tex]
Hence, option C is correct.
To learn more about the mean concept, you can take a look at https://brainly.com/question/13451786