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