A city government estimates that they must accrue $1.5 million per employee to finance each employee's retirement pension. If each employee works for an average of 30 years, how much per employee would the city have to invest today? Assume a discount rate of 10%. Then, calculate the amount needed per employee if the discount rate is not 10%, but 6%. If the workforce numbers 3,000, what is the total difference in cost between these two assumptions?