4a) In a perpetual inventory system, the Cost of Goods Sold account is used a. only when a cash sale of merchandise occurs. b. only when a credit sale of merchandise occurs. c. only when a sale of merchandise occurs. d. whenever there is a sale of merchandise or a return of merchandise sold. 4b) Martin Company reported the following balances at June 30, 2020: Sales Revenue $16,500 Sales Returns and Allowances 800 Sales Discounts 200 Cost of Goods Sold 7,100 How much were the net sales for the month