Investing in inventory. Calculate the average investment in inventory for each of the following situations. Assume a 365-day year. (a) A firms annual sales are $18 million, its gross profit margin is 32%, and its average age of inventory is 45 days. (b) A firms annual sales are $325 million, its cost of goods sold is 80% of sales, and it turns its inventory 10 times per year. (c) A firms annual cost of goods sold totals $120 million, and it turns its inventory about every 70 days.