Answer:
(a)Merchandising Business
            Music World Retail
Income statement at December 31, 2017 (extract)
Cost of Goods Sold
Beginning inventory Merchandise        145,000
Add Cost of purchases                 340,000
Less  Ending inventory Merchandise      (120,000)
Cost of Goods Sold                    365000
(a)Manufacturing Business
            Wave-Board Manufacturing
Income statement at December 31, 2017 (extract)
Cost of Goods Sold
Beginning Finished goods              350,000
Add Cost of goods manufactured        590,000
Less Finished goods                   (170,000)
Cost of Goods Sold                    770000
Explanation:
(a)Merchandising Business
Music World Retail is in the Merchandising Business and its Cost of Sales will account for cost of merchandise purchased.
(a)Manufacturing Business
Wave-Board Manufacturing is in the Manufacturing Business and its Cost of Sales will account for cost of Finished Goods transferred from the Manufacturing Account