If variable manufacturing costs are $13 per unit and total fixed manufacturing costs are $270,000, what is the manufacturing cost per unit ir a. 4,500 units are manufactured and the company uses the variable costing concept? b. 6,000 units are manufactured and the company uses the variable costing concept? c. 4,500 units are manufactured and the company uses the absorption costing concept? d. 6,000 units are manufactured and the company used the absorption costing concept