Where are they getting the 6,000 from the cost of goods sold entry?

6:54 AM accountinginfo.com Verizon Example 1 (Company A On May 1, 2016: Purchased 1,000 units of merchandise at $30 per unit. Under Perpetual inventory system S/1/2016 Merchandise Inventory Accourts payable Under Periodic inventory system Accounts payable Under periodic inventory system, all purchases during the accounting period are recorded in the "Purchases" account. On May 6, 2016: Sold 200 units of merchandise at $50 per unit on credit. Under Perpetual inventory system S/1/2016 Cost of goods sold 6,000 Under perpetual inventory system, account are after each Under Periodic inventory system VL/2016 Accounts Receivable Under periodic inventory system, the following journal entry is recorded at the end of accounting period 5/31/2016 Merchandise Inventory Quantity of merchandise inventory = 1,000 units purchased-200 units sold = 800 units left Cost of merchandise inventory = 800 units x $30 per unit cost = $24,000 5/31/2016 Cost of goods sold