Concept:The cost of goods sold formula links opening stock, purchases, and closing stock. Rates and wages are not needed here.Explanation:Cost of goods sold is calculated as:Cost of goods sold=Opening stock+Purchases−Closing stockRearrange to find purchases:Purchases=Cost of goods sold−Opening stock+Closing stockSubstitute the values for 2008:Opening stock =N4200Closing stock =N3900Cost of goods sold =N6000Thus:Purchases=N6000−N4200+N3900Purchases=N1800+N3900Purchases=N5700Answer:D. N5 700