In this chapter, we learned that the quantity of U.S. currency outstanding was $3,490 in March 2012. Suppose that we were to try to use this number to estimate the amount of output produced in the underground economy in the United States during 2009. Discuss how we would use this information on the quantity of currency in circulation, and what additional information you would want to have to come up with a good estimate. In your answer, you will need to consider how underground transactions might take place by other means in the United States than through the use of U.S. currency, and how some of U.S. currency is not being used for underground transactions in the United States.