If variable cost of goods sold totaled $65,452 for the year (16,363 units at $4 each) and the planned variable cost of goods sold totaled $98,273 (14,039 units at $7 each), the effect of the quantity factor on the change in contribution margin is:

a.$9,296 decrease

b.$16,268 increase

c.$16,268 decrease

d.$9,296 increase