If variable selling and administrative expenses totaled $120,000 for the year (80,000 units at $1.50 each) and the planned variable selling and administrative expenses totaled $136,500 (78,000 units at $1.75 each), the effect of the unit cost factor on the change in contribution margin is:

a.	$20,000 increase
b.	$19,500 decrease
c.	$19,500 increase
d.	$20,000 decrease