The 2010 income statement of Holly Enterprises shows operating revenues of $134,800, selling expenses of $38,310, general and administrative expenses of $36,990, interest expense of $580 and income tax expense of $13,920. Holly's stockholders' equity was $280,000 at the beginning of the year and $320,000 at the end of the year. The company has 20,000 shares of stock outstanding at December 31, 2010. What is the company's profit margin ?