A firm faces a demand of 2,600 units per month for one of its lines of stock. The firm's cost of holding stock is 4 per unit of average stock per month. In addition, it costs the firm a total of 40 every time it orders and acquires a new shipment of stock, and 6 per unit of average stock-out. If the firm is willing to face stock-outs, and attempts to minimise overall inventory- related costs, the firm's monthly total inventory-related costs are approximately: A. 707 B. 852 C. 913 D. 981