Jackson Corporation has provided the following for three months of income statements: July August September Sales in Units Sales 500 1000 800 250,000 500,000 400,000 Less: cost of goods sold 125,000 250,000 200,000 Gross margin 125,000 250,000 200,000 Operating expenses: Advertising 5,000 5,000 5,000 Salaries & Commissions 72,500 85,000 80,000 Depreciation expense 10,000 10,000 10,000 Utilities expense 12,000 17,000 15,000 Total operating expenses 99,500 117,000 110,000 Net Income 25,500 133,000 90,000 Classify each of the company's expenses as variable, fixed, or mixed.