Apple's 2019 10K Inventory Calculations?

I'm trying to calculate the following for Apple from its 2019 10K, but I don't know if I'm doing the calculations correctly.

I'm trying to calculate the following:

Days Sales of Inventory
Inventory Turnover
Inventory to Sales Ratio
Sales Vs. Receivables
Cash Flow from Operations
Return on Equity

I used the following formulas:

• 1. First, calculate the company’s Days Sales of Inventory (DSI):
     a. To calculate the company’s days sales of inventory, I used the following formula: Average Inventory (a.k.a, ending inventory) / COGS (aka total cost of sales) * 365
     For Apple, I used (Average Inventory of $4,106 / Total Cost of Sales of $161,782)*365 = 9.23 DSI
• 2. Second, calculate the company’s Inventory Turnover:
     a. To calculate the company’s inventory turnover, I used the following formula: Sales / Average Inventory, (where average inventory is beginning inventory – ending inventory / 2).
     For Apple, I used net income of $55,256 / inventories of $4,106 = 1.35
• 3. Third, calculate the company’s Inventory to Sales Ratio:
     a. To calculate the company’s inventory to sales ratio, I used the following formula: average inventory / net sales, (where average inventory = beginning inventory + ending inventory / 2), (and where net sales = gross sales – returns).
     For Apple, I used inventories of $4,106 / net income of $55,256 = 0.07

• How to Calculate Sales vs Receivables:

• 1. First, calculate the company’s Accounts Receivable to Sales Ratio:
     a. To calculate the company’s accounts receivable to sales ratio, I used the following formula: accounts receivable / sales, (where accounts receivable refers to sales that have occurred on credit, meaning that the company has not yet collected the cash proceeds from these sales. Found in the “current assets” section of the balance sheet.), and (the sales refer to all sales that the company has realized over the given accounting period, including sales on credit and cash sales. Found on the income statement.)
     For Apple, I used the “accounts receivable, net” of $22,926 / the “total comprehensive income” of $58,037 from the income statement = 0.40

• How to Calculate Cash Flow from Operations:

• 1. First, calculate the company’s Operating Cash Flow:
     a. To calculate the company’s operating cash flow, I used the following formula: Operating Cash Flow = Operating Income + Depreciation – Taxes + Change in Working Capital
     For Apple, I used operating income of $63,930 from the profit & loss statement + depreciation and amortization of $ 12,547 from the cash flow statement – provision for income taxes of $10,481 from the profit & loss statement + change in working capital of $57,101 (from total current assets of $162,819 – total current liabilities of $105,718) = $123,097 M

• How to Calculate Return on Equity:

• 1. First calculate the company’s Return on Equity:
     a. To calculate the company’s return on equity, I used the following formula: ROE = Net Income / Shareholder’s Equity
     For Apple, I used net income of $55,256 / shareholder’s equity of $90,488 = 0.61

Any assistance would be greatly appreciated.

Thank you,

djb5595