Please show the steps with the formula. Thank you.

Riverbed Corporation sells one product, with information for July as follows: Riverbed uses the FIFO cost formula. All purchases and sales are on account. Ignore any estimated returns on purchases and sales. Record journal entries in the order presented in the problem.) July 20 Purchases Accounts Payable July 27 Accounts Receivable Sales Revenue July 31 Inventory Cost of Goods Sold Purchases 2624 2624 2090 2090 4880 262 5084 (b) Your answer is incorrect. Calculate gross profit using the periodic system. Gross profit / (loss) $