please explain this adjusting entry, the adjusting entry on number 2

ons and inting of Prepare the adjusting entries at December 31, 2017. (Show all computations.) P3-5A On September 1, 2017, the account balances of Beck Equipment Repair, Ltd. were as follows. No. Debit No. Credit 101 Cash 5,020 158 Accumulated Depreciation Equipment 2,240 112 Accounts Receivable 3,520 201 Accounts Payable 3,400 126 Supplies 2,000 209 Unearned Service Revenue 1,400 157 Equipment 18,000 212 Salaries and Wages Payable 500 311 Share Capital-Ordinary 10,000 320 Retained Earnings 11,000 28,540 28,540 During September, the following summary transactions were completed. Sept. 8 Paid 1,700 for salaries due employees, of which 1,200 is for September salaries. 10 Received 1,200 cash from customers on account. 12 Received 3,400 cash for services performed in September. 15 Purchased store equipment on account 3,000. 17 Purchased supplies on account 1,900. 20 Paid creditors 4,500 on account. 22 Paid September rent 500. 25 Paid salaries 1,360. 27 Performed services on account and billed customers 1,600 for those services. 29 Received 750 from customers for future service. Adjustment data consist of: 1. Supplies on hand 1,700. 2. Accrued salaries payable 400. 3. Depreciation is 140 per month. 4. Services related to unearned service revenue of 1,450 were performed. Trans. Particulars Debit in Credit in 1 Supplies Expense a/c Dr. 2200 To Supplies 2200 (Supplies expensed) 2000 + 1900 - 1700