Why is the demand curve referred to as a marginal benefit curve?

On september 12, ryan company sold merchandise in the amount of $5,800 to johnson company, with credit terms of 2/10, n/30. the cost of the items sold is $4,000. ryan uses the periodic inventory system and the net method of accounting for sales. on september 14, johnson returns some of the non-defective merchandise, which is restored to inventory. the selling price of the returned merchandise is $500 and the cost of the merchandise returned is $350. the entry or entries that ryan must make on september 14 is (are): multiple choice sales returns and allowances 490 accounts receivable 490 merchandise inventory 350 cost of goods sold 350 sales returns and allowances 490 accounts receivable 490 sales returns and allowances 500 accounts receivable 500 sales returns and allowances 490 accounts receivable 490 merchandise inventory 343 cost of goods sold 343 sales returns and allowances 350 accounts receivable 350