The Equipment Maintenance Department of Airedale Company incurred costs during the past year. For Airedale, the differences between the units produced at the highest level of production was 1,000 units (2,000 units - 1,000 units). The difference between the total costs at the highest level of production was $20,000 ($50,000 - $40,000. Using the high-low method, the estimated unit variable cost is OA) $10 B) $20 C) $30 D) $40 E) none of the above