Derive a closed-form formula for finding the accumulated sum F at the end of n years that will result from a series of beginning-of-year payments each equal to A if the latter are placed in a fund for which the interest rate is i compounded yearly. Find Ffor A = $15,000, n = 20 years and i = 0.10 (i.e., 10% rate of interest compounded yearly). What is the present worth of this annuity