Amazon.com, Inc. had the following information for the year 2023:

• Beginning Inventory: $30 billion
• Purchases: $90 billion
• Ending Inventory: $40 billion Calculate: a) Cost of Goods Sold (COGS). b) Inventory Turnover Ratio. c) Days Sales Outstanding (DSO) if the accounts receivable at the beginning of the year were $50 billion and at the end of the year were $60 billion.