Detailed Answer
Answer (C) is correct. The gross profit (gross margin) method calculates ending inventory at a given time by subtracting an estimated cost of goods sold from the sum of beginning inventory and purchases (or cost of goods manufactured). The estimated cost of goods sold equals sales minus the gross profit. The gross profit equals sales multiplied by the gross profit percentage, an amount ordinarily determined on a historical basis. Given that the gross margin percentage is 40% of net sales, cost of goods sold must be 60% of net sales, or $540,000 ($900,000 x 60%). Goods available for sale equals cost of goods sold plus ending inventory ($540,000 + $200,000 = $740,000)