Just the last question please? with explanation :)

At the beginning of the current period, Marx Corporation had balances in Accounts Receivable of $160,000 and in Allowance for Expected Credit Losses of $7,200 (credit). During the period, Marx had credit sales of $640,000 and collections on account of $610,400. Marx expects a return rate of 5%. Marx uses a perpetual inventory system and determined that the cost of goods sold during the period was $536,000. Marx wrote off as uncollectible, accounts receivable of $5,600. However, a $2,400 account previously written off as uncollectible was recovered before the end of the current period. Uncollectible accounts are estimated to total $20,000 at the end of the period. (a) Your answer is correct. Prepare the entries to record sales, cost of goods sold, and collections during the period. (List all debit entries before credit entries. Credit account titles are automatically indented when amount is entered. Do not indent manually. If no entry is required, select "No Entry" for the account titles and enter 0 for the amounts.) (b) Prepare the entry to record the write-off of uncollectible accounts during the period. (List debit entry before credit entry. Credit account titles are automatically indented when amount is entered. Do not indent manually. If no entry is required, select "No Entry" for the account titles and enter 0 for the amounts.) required, select "No Entry" for the account titles and enter 0 for the amounts.) (d) Prepare the entry to record credit losses for the period. (List debit entry before credit entry. Credit account titles are automatically indented when amount is entered. Do not indent manually. If no entry is required, select "No Entry" for th account titles and enter 0 for the amounts.)