Jackson Grills Has Supplied the Following Information from Its Accounting

Jackson Grills has supplied the following information from its accounting records for the month of August.
Direct labour cost $11,500
Purchases of raw materials 20,000
Factory depreciation 7,500
Advertising 10,000
Factory property taxes 6,500
Materials inventory, 8/1 1,250
Materials inventory, 8/31 2,500
Work-in-process inventory, 8/1 ?
Work-in-process inventory, 8/31 1,500
Cost of goods manufactured 45,850
Sales revenue ?
Executive salary cost 25,000
Finished goods inventory, 8/1 5,500
Finished goods inventory, 8/31 4,250
Operating income 67,900
Gross margin ?
Required: Solve for the missing amounts (?).