18. What is the future value of a series of $4,500 annual payments received at the end of each of the next 6 years' worth if they are invested at an annual rate of return of 7%? 19. Repeat above question for annuity due. 20. Sultan's Used Cars just sold you a clunker (you need it to get to class on time). You financed the $8,000 purchase price for 48 months. They said your payment would be $250. What interest rate did they charge you (assume monthly compounding)