Amazon.com, Inc. disclosed the following income statement figures for the year ended December 31, 2023. Net sales amounted to $469,814 million, with a cost of sales of $310,263 million, resulting in a gross profit of $159,551 million. Operating expenses totaled $133,434 million, leading to an operating income of $26,117 million. After accounting for interest expenses of $1,677 million and income tax expenses of $7,689 million, Amazon.com, Inc. reported a net income of $20,143 million.

a. Calculate Amazon.com, Inc.'s gross profit margin. b. Determine the operating income margin for Amazon.com, Inc. c. Discuss the impact of Amazon.com, Inc.'s interest expense on its profitability. d. Analyze the effective tax rate of Amazon.com, Inc. and its implications for investors.