An explanation if possible is greatly appreciated!

Required information [The following information applies to the questions displayed below.] The transactions listed below are typical of those involving New Books Inc. and Readers' Corner. New Books is a wholesale merchandiser and Readers' Corner is a retail merchandiser. Assume all sales of merchandise from New Books to Readers' Corner are made with terms n/30, and the two companies use perpetual inventory systems. Assume the following transactions between the two companies occurred in the order listed during the year ended August 31. a. New Books sold merchandise to Readers' Corner at a selling price of $640,000. The merchandise had cost New Books $451,000. b. Two days later, Readers' Corner complained to New Books that some of the merchandise differed from what Readers' Corner had ordered. New Books agreed to give an allowance of $12,500 to Readers' Corner. Readers' Corner also returned some books, which had cost New Books $3,800 and had been sold to Readers' Corner for $5,300. C. Just three days later, Readers' Corner paid New Books, which settled all amounts owed. Required: 1. For each of the events (a) through (c), indicate the amount and direction of the effect on New Books in terms of the following items. (Enter any decreases to account balances with a minus sign.) Answer is complete but not entirely correct. Transaction Sales Returns Sales Allowances Net Sales Sales Revenues 640,000 Cost of Goods Sold Gross Profit a. 451,0 5,300 b. 3,800 x 640,000 (17,800) 17,800 12,500 189,000 12,500 17,800 C. 17,800 0