If variable cost of goods sold totaled $80,490 for the year (16,098 units at $5 each) and the planned variable cost of goods sold totaled $115,816 (14,477 units at $8 each), the effect of the quantity factor on the change in contribution margin is: Ca. $8,105 decrease Ob. $8,105 increase c. $12,968 decrease Od. $12,968 increase