If variable manufacturing costs are $9 per unit and total fixed manufacturing costs are $323,400, what is the manufacturing cost per unit if: a. 4,900 units are manufactured and the company uses the variable costing concept? $ b. 6,600 units are manufactured and the company uses the variable costing concept? $ c. 4,900 units are manufactured and the company uses the absorption costing concept? $ d. 6,600 units are manufactured and the company uses the absorption costing concept? $