STU Corporation's financial statements reveal:

• Total assets: $1,200,000
• Total liabilities: $350,000
• Common stock: $500,000
• Additional paid-in capital: $200,000
• Retained earnings: $250,000
• Net income: $200,000
• Total revenues: $900,000

Calculate: a) Debt-to-equity ratio b) Dividend yield c) Return on investment d) Operating profit margin