Company X produced and sold 1,000 units during the month of April. The company incurred the following expenses: direct materials $5,000, direct labor $8,000, total manufacturing overhead cost $20,000, total selling and administrative cost $30,000. Assume that 85% of the total manufacturing overhead cost and 30% of the total selling and administrative costs was variable cost, calculate the variable manufacturing cost per unit. a. 30 O b. 21 c. 13 O d. 63 e. 33