Accounting/financial - Please help on Calculation of $$$ have to

Accounting/financial - Please help on Calculation of $$$ have to be reserved for business operation.

Here are the steps I did.

1. calculate A/R turnover – net sale/(open receivable + close receivable)/2
2. calculate average days revenue in Receivables – 365/step 1
3. calculate average daily cost – I use the total year cost /365
4. step 2 x step 3 = $$$$ need be reserved

I am not confident on step 3 and step 4. Please let me know if it is correct. Thanks for your help.