Harper Ltd has observed that at an activity level of 8 000 units the maintenance cost is $28 000, and at 12 000 units the maintenance cost is $36 000. Using the high-low method, the cost formula for maintenance is Select one a. $12000+ $1.50 x units. b. $12000 - $2.00 x units. O c 54000 - $2.00 x units. d. $3.00/unit