The correct answer is A. 15%.
Net profit ratio is calculated by dividing net profit by sales. In this case, net profit is calculated by subtracting cost of sales and indirect expenses from sales. This gives us a net profit of Rs. 80,000. Dividing this by sales of Rs. 8,00,000 gives us a net profit ratio of 15%.
Option B is incorrect because it is the gross profit ratio, which is calculated by dividing gross profit by sales. Gross profit is calculated by subtracting cost of goods sold from sales. In this case, gross profit is Rs. 3,20,000. Dividing this by sales of Rs. 8,00,000 gives us a gross profit ratio of 40%.
Option C is incorrect because it is the operating profit ratio, which is calculated by dividing operating profit by sales. Operating profit is calculated by subtracting operating expenses from gross profit. In this case, operating profit is Rs. 200,000. Dividing this by sales of Rs. 8,00,000 gives us an operating profit ratio of 25%.
Option D is incorrect because it is the return on assets ratio, which is calculated by dividing net profit by total assets. In this case, total assets are not given, so we cannot calculate the return on assets ratio.