How is zakat calculated on a commercial store that has inventory, debts owed to it, and debts owed by it, and when is its lawful time of payment?

If a year (hawl) has passed on the merchandise, appraise it at its current market value. Add the expected receivables, deducting them from the outstanding debts owed to others. If the remaining amount reaches the threshold (nisab) of gold (85 grams), then zakat becomes obligatory; otherwise, it does not. The zakat year is the lunar year.