Carver Company produces a product which sells for $30. Variable manufacturing costs are $15 per unit. Fixed manufacturing costs are $5 per unit based on the current level of activity, and fixed selling and administrative costs are $4 per unit. A selling commission of 10% of the selling price is paid on each unit sold. The contribution margin per unit is: a. $3 

b. $15 

c. $8 

d. $12