Calculate 3M's (ticker: U:MMM) total annual cost of resources invested in accounts receivable in each of the last five years. Assume that there are no fixed costs, that is, all costs are variable costs (use COGS and SG&A). Calculate 3M's average investment in accounts receivable in each year. Using 3M's WACC as a measure of equal-risk opportunity cost of the investment in accounts receivable, calculate the total annual cost of resources invested in accounts receivable. Has this cost decreased or increased over the years? Since these exercises depend upon real-time data, your answers will change continuously depending upon when you access the Internet to download your data.