Sterling Corporation reports the following information: 2009 2010 2011 Units sold 20,000 20,000 20,000 Units produced 20,000 24,000 16,000 Fixed production costs $1,200,000 $1,200,000 $1,200,000 Variable production costs per unit $200 $200 $200 Selling price per unit $400 $400 $400 Fixed selling and administrative expenses $400,000 $400,000 $400,000 Calculate the profit each year using variable costing. Explain why profit does not fluctuate from year to year using variable costing.