I can't figure out the last entry: "Record the end of period adjustment"

Thank you!

Sigfusson Supplies reported beginning inventory of 90 units, for a total cost of $3,150. The company had the following transactions during the month: January 6 Sold 20 units on account at a selling price of $45 per unit. January 9 Bought 10 units on account at a cost of $35 per unit. January 11 Sold 10 units on account at a selling price of $50 per unit. January 19 Sold 20 units on account at a selling price of $55 per unit. January 27 Bought 10 units on account at a cost of $35 per unit. January 31 Counted inventory and determined that 45 units were on hand. quired: Prepare the journal entries that would be recorded using a periodic inventory system. (If no entry is required for a transaction/event, select "No Journal Entry Required" in the first account field.) Journal entry worksheet 1 2 3 4 5 6 Record the end of period adjustment to determine the amount of cost of goods sold, including any "book-to-physical" adjustment that might be needed