If variable manufacturing costs are $15 per unit and total fixed manufacturing costs are $303,800, what is the manufacturing cost per unit if: a. 4,900 units are manufactured and the company uses the variable costing concept? $ b. 6,200 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. 6,200 units are manufactured and the company uses the absorption costing concept? $