Amazon.com, Inc. reported the following financial details for 2023: total revenue of $500 billion, with a cost of goods sold amounting to $300 billion. Their operating expenses were $150 billion, and they incurred an interest expense of $8 billion and a tax expense of $15 billion. The total assets of the company stood at $600 billion while the total liabilities were $250 billion.

1. Calculate the gross profit margin.
2. Determine the operating profit margin.
3. Compute the interest coverage ratio.
4. Determine the return on assets (ROA).