If variable cost of goods sold totaled $66,560 for the year (16,640 units at $4 each) and the planned variable cost of goods sold totaled $100,450 (14,350 units at $7 each), the effect of the unit cost factor on the change in contribution margin is: a. $9,160 increase b. $49,920 increase c. $9,160 decrease d. $49,920 decrease