Gridiron Merchandising anticipated selling 30,000 units of a major product and paying sales commissions of $8 per unit. Actual sales and sales commissions totaled 30,500 units and $253,100, respectively. If the company used a flexible budget for performance evaluations, Gridiron would report a cost variance of:

$9,100U.

$9,100F.

$13,100U.

$13,100F.

None of these. *show your work*