A company produces a single product. Variable production costs are $12 per unit and variable selling and administrative expenses are $3 per unit. Fixed manufacturing overhead totals $36,000 and fixed selling and administration expenses total $40,000. Assuming a beginning inventory of zero, production of 4,000 units and sales of 3,600 units, the dollar value of the ending inventory under variable costing would be:

a. $3,600

b. $8,400

c. $4,800

d .$6,000