Gamma Company produces a single product. During the year just ended, the company's net operating income under absorption costing was $3,000 lower than under variable costing. The company sold 9,000 units during the year, and its variable costs were $9 per unit, of which $3 was variable selling expense. If production cost is $11 per unit under absorption costing every year, then how many units did the company produce last year? A. 8,000 B. 10,000 C. 9,600 D. 8,400