72. (Spreadsheet helpful) You think what your roommate means in Exercise 71 is that she wants to retire in 2050 with a steady income of $100,000 a year in 2015 dollars. You also feel that she should plan to receive that same value of income for 43 years in case she lives to 100 (2% of your classmates will). What is the present value in 2015 of the planned stream of 43 years of retirement income?