Pfizer Inc. had the following information for the year 2023:

4. 
   
   • Beginning Inventory: $10 billion
   • Purchases: $45 billion
   • Ending Inventory: $15 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 $20 billion and at the end of the year were $30 billion.