Please Explain

A company's total overhead cost at various levels of activity is presented below: Assume that the overhead cost above consists of utilities, supervisory salaries, and maintenance. The breakdown of these costs at the 4,000 machine-hour level of activity is as follows: Suppose the company uses the high-low method to estimate a cost formula for maintenance. What is the total maintenance cost the company expects to incur at an activity level of 7, 600 machine hours? a. $12, 640 b. $13, 400 c. $12, 800 d. $11, 500 e. None of the above