Question 5 (optional): bonus question. (5 points) Suppose a series of equal $10,000 withdrawals, the first occuring now (at time t = 0), and the remaining ones occuring successively in 4, 8, 12, and 16 years from now. The interest rate is 10%. Using a single factor, find the equivalent annual worth of this cash flow up to year 20, i.e. find the equivalent uniform series spanning from year 1 to 20. Write the expression of the annual worth (i.e. using no more than a single factor)