McDonald's Corporation reported the following financial information for the year ending December 31, 2023:

• Total Revenue: $90 billion
• Cost of Goods Sold (COGS): $40 billion
• Operating Expenses: $30 billion
• Other Income: $5 billion
• Tax Expense: $15 billion

a) Calculate the gross profit. b) Determine the operating profit. c) Compute the net profit before tax. d) Calculate the net profit after tax, assuming a tax rate of 20%.