Which one of the following will increase the profit margin of a firm all else constant?

To increase the profit margin of a firm while keeping everything else constant, the firm can either reduce its costs or increase its selling prices. Lowering costs, such as reducing operational expenses or negotiating better rates with suppliers, directly improves the profit margin. Alternatively, increasing selling prices without affecting sales volume can also enhance the profit margin. However, any pricing strategy must consider market demand and competition to avoid potential loss in sales.