My question relates to Part A. I know the answer is 25 (20 + 4 + 1), but my question is... why is sales commission (a variable cost) not included in the inventoriable cost per unit? Please explain. Thank you!!

Achilles Auto makes and sells batteries. In 2017, it made 100,000 batteries and sold 9-1 75,000 of them, at an average selling price of $60 per unit. The following additional information relates to Achilles Auto for 2017: Direct materials Direct manufacturing labor Variable manufacturing costs Sales commissions Fixed manufacturing costs Administrative expenses, all fixed $ 20.00 per unit $ 4.00 per unit $ 1.00 per unit $ 6.00 per part $750,000 per year $270,000 per year What is Achilles Auto's inventoriable cost per unit using (a) variable costing, and (b) absorption costing