15. About how many years would it take for your investment to grow tenfold if it were invested at 12% compounded semiannually?

16. You plan to deposit $400 at the end of each year for 2 years, $200 at the end of next year, $300 at the end of each year for the next 3 years, and $100 at the end of each year for the last 2 years. How much will you have over the entire period if your savings account awards 4% per year?

18. What is the face value of a loan with twelve-equal payments of $12,000 each year if the first payment that the bank will receive is 10 years from now and the discounted rate is 10%?