Tirri Corporation has provided the following information: Cost per Unit Cost per Period Direct materials $ 6.70 Direct labor $ 3.50 Variable manufacturing overhead $ 1.20 Fixed manufacturing overhead $ 22,800 Sales commissions $ 1.15 Variable administrative expense $ 0.50 Fixed selling and administrative expense $ 7,200 If the selling price is $26.50 per unit, the contribution margin per unit sold is closest to