The computation follows:
1. Solve first for the variable cost per unit.
Direct materials $ 6.00
Direct labor $ 3.50
Variable manufacturing overhead $ 1.50
Sales commissions $ 1.00
Variable administrative expense $ 0.50
= $12.50 variable cost per unit
2. Then deduct the selling price to the variable cost per unit, to get the contribution margin.
22 - 12.50 = $9.50 CM per unit