For the year 2023, Frontier Airlines reported total revenue of $50 million, cost of services of $30 million, operating expenses of $12 million, interest expense of $2 million, and tax expense of $2 million. The company’s total assets were $60 million, and total liabilities were $25 million.

1. Calculate the operating profit margin.
2. Determine the net profit margin.
3. Compute the debt-to-equity ratio.
4. Determine the return on equity (ROE).