As you can see I have the answers to this question, but I don't understand where the 2000 comes from in the second box of # number of units sold comes from. If someone could break down the math to how this is solved I would appreciate it.

Required information [The following information applies to the questions displayed below.] Ferris Company began January with 8,000 units of its principal product. The cost of each unit is $9. Merchandise transactions for the month of January are as follows: Date of Purchase Jan. 10 Jan. 18 Totals Units 5,000 8,000 13,000 Purchases Unit Cost* $ 10 11 Total Cost $ 50,000 88,000 138,000 * Includes purchase price and cost of freight. Sales Date of Sale Jan. 5 Jan. 12 Jan. 20 Total Units 3,000 3,000 4,000 10,000 11,000 units were on hand at the end of the month. Required: 1. Calculate January's ending inventory and cost of goods sold for the month using FIFO, periodic system. Ending Inventory - Periodic FIFO FIFO Cost of Goods Available for Sale Cost # of Cost of Goods units per unit Available for Sale 8,000 $9.00 S72,000 Cost of Goods Sold - Periodic FIFO # of Cost Cost of units Goods sold per unit Sold 8,000 S 9.00 S 72,000 # of units in ending inventory Cost per unit Ending Inventory 0 $ 9.00 $ 0 Beginning Inventory Purchases: January 10 5,000 10.00 50,000 2,000 S 10.00 20,000 3,000 $ 10.00 30,000 January 18 8,000 88,000 S 11.00 11.00 0 8,000 $ 11.00 88,000 Total 21,000 $ 210,000 10,000 S 92,000 11,000 $ 118,000