need help with this cant seem to understand what im doing on the last portion of this

Required information [The following information applies to the questions displayed below.] Sigfusson Supplies reported beginning inventory of 100 units, for a total cost of $2,000. The company had the following transactions during the month: January 6 Sold 30 units on account at a selling price of $30 per unit. January 9 Bought 20 units on account at a cost of $20 per unit. January 11 Sold 20 units on account at a selling price of $35 per unit. January 19 Sold 30 units on account at a selling price of $40 per unit. January 27 Bought 20 units on account at a cost of $20 per unit. January 31 Counted inventory and determined that 40 units were on hand. Required: 1. 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.) Required information \begin{tabular}{|c|c|c|c|c|c|} \hline No & Date & \multicolumn{2}{|c|}{ General Journal } & Debit & Credit \\ \hline \multirow[t]{2}{*}{1} & January 06 & Accounts Receivable & & 900 & \\ \hline & & Sales Revenue & & & 900 \\ \hline \multirow[t]{2}{*}{2} & January 09 & Purchases & & 400 & \\ \hline & & Accounts Payable & & & 400 \\ \hline \multirow[t]{2}{*}{3} & January 11 & Accounts Receivable & & 700 & \\ \hline & & Sales Revenue & & & 700 \\ \hline \multirow[t]{2}{*}{4} & January 19 & Accounts Receivable & & 1,200 & \\ \hline & & Sales Revenue & & & 1,200 \\ \hline \multirow[t]{2}{*}{5} & January 27 & Purchases & & 400 & \\ \hline & & Accounts Payable & & & 400 \\ \hline \multirow[t]{4}{*}{6} & January 31 & Cost of Goods Sold & & 2,800 & \\ \hline & & Purchases & & x & 800 \\ \hline & & Inventory, Beginning & & & 2,000 \\ \hline & & & x & & \\ \hline \end{tabular} *Red text indicates no response was expected in a cell or a formula-based calculation is incorrect; no points deducted