If variable cost of goods sold totaled $100,500 for the year (16,750 units at $6 each) and the planned variable cost of goods sold totaled $115,280 (14,410 units at $8 each), the effect of the unit cost factor on the change in contribution margin is: a. $33,500 increase b. $14,040 increase c. $14,040 decrease d. $33,500 decrease