28. The following table shows the spot rates of interest over a number of hori zons: Period of investment in years) Spot rate (in %) 6.00 7.00 7.75 8.25 (a) Find the present value of payments of $100 at the end of each year for 4 years. (b) What is the effective rate of interest earned by this annuity-immediate if it were constant through the whole investment period? (Hint: Use the Excel function Rate to compute the rate of interest.]