Concept:Mark-up is profit as a fraction of cost of sales, while margin is profit as a fraction of sales.Explanation:Given mark-up =31, profit is 31 of cost of sales.Therefore, margin =cost of sales+profitprofit=3+11=41.Since sales =Le 180,000, we have:41=180,000profitProfit=4180,000=Le 45,000Cost of sales = Sales − Profit =180,000−45,000=Le 135,000.Now use: Cost of sales = Opening stock + Purchases − Closing stock.135,000=6,000+Purchases−4,200Purchases=135,000+4,200−6,000=Le 133,200Answer:C. Le 133,200.