Please help me understand what is supposed to go in the red boxes?

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Culver Warehouse distributes hardback books to retail stores and extends credit to all of its customers. During the month of June, the following merchandising transactions occurred. June 1 Purchased books on account for $2,490 from Catlin Publishers. 3 Sold books on account to Garfunkel Bookstore for $1,400. The cost of the merchandise sold was $900. 6 Received $90 credit for books returned to Catlin Publishers. 9 Paid Catlin Publishers in full. 15 Received payment in full from Garfunkel Bookstore. 17 Sold books on account to Bell Tower for $1,400. The cost of the merchandise sold was $800. 20 Purchased books on account for $900 from Priceless Book Publishers. 24 Received payment in full from Bell Tower. 26 Paid Priceless Book Publishers in full. 28 Sold books on account to General Bookstore for $2,650. The cost of the merchandise sold was $850. 30 Granted General Bookstore $260 credit for books returned costing $90. Prepare a tabular summary to record the transactions for the month of June for Culver Warehouse using a perpetual inventory system. Include margin explanations for the changes in revenues and expenses. (Enter negative amounts using either a negative sign Prepare a tabular summary to record transactions of Sheridan's Books listed below. Assume Sheridan's uses a perpetual inventory system. July 6 Purchased $1,460 of merchandise on credit, terms n/30. 8 Returned $92 of the items purchased on July 6. 19 Sold merchandise on credit for $4,060, on account. The merchandise had an inventory cost of $2,460. 22 Of the merchandise sold on July 19,$300 of it was returned. The items had cost the store $138. 28 Received payment in full from the customer of July 19. 31 Paid for the merchandise purchased on July 6. (Enter negative amounts using either a negative sign preceding the number e.g. -45 or parentheses e.g. (45).)