Retleb Manufacturing Company noticed that, during its busiest month of 20xx, maintenance costs totaled $15,400, resulting from the production of 32,000 units. During its slowest month, $12,600 in maintenance costs were incurred, resulting from the production of 24,000 units. Using the high-low method, what maintenance cost would the company expect to incur at a volume of 20,000 units?
a. $7,000
b. $11,200
c. $8,400
d. $2,800