If variable manufacturing costs are $15 per unit and total fixed manufacturing costs are $393,300, what is the manufacturing cost per unit if: a. 5,700 units are manufactured and the company uses the variable costing concept? b. 6,900 units are manufactured and the company uses the variable costing concept? c. 5,700 units are manufactured and the company uses the absorption costing concept? d. 6,900 units are manufactured and the company uses the absorption costing concept?