1. Equipment used in operations cost $420,000; it was purchased on July 1, 2017. It has an estimated useful life of 12 years. Straight-line depreciation is used. 2. The company estimates an increase in Allowance for Doubtful Accounts of $3,000 is required to recognize accounts receivable of $300,000 at net realizable value. 3. At the beginning of 2020, office supplies amounted to $600. During 2020, office supplies of $8,800 were purchased; this amount was debited to Office Supplies Expense. An inventory of office supplies at the end of 2020 showed $400 still available. However, the January 1 balance of $600 is still recorded in the Office Supplies account. 4. On July 1, 2020, the company paid a three-year insurance premium of $2,160; this amount was debited to Prepaid Insurance. 5. On August 1, 2020, the company borrowed $120,000 cash from Shar Bank. The loan was for 12 months at 9% interest payable at maturity date. 6. On December 31, 2020, salaries earned by employees but not yet paid (or recorded) was $18,000. Prepare the adjusting entry (or entries) that are necessary, if any, on December 31, 2020, for each item 1 through 6. Note: If a journal entry isn't required for the transaction, select "N/A" as the account names and leave the Dr. and Cr. answers blank (zero).