please show what formulas you use, and why! detailed the better!

You walk into the bank and see a sign advertising a CD special - this week only. It offers 5.5% per year on any investment of 4 years. You check your bank account balance and decide you can afford to invest $500 and you buy the CD (spend the $500 on a CD). What is the total value of the account (including interest) after 4 years? Assume reinvestment of interest each year. Your best friend graduated last year and now works for an insurance company, selling investment products. He was asked to find out what young people might be willing to offer for a new product that the insurance company calls "Plain vanilla." They hope it will be attractive to young investors that wish to start with simple investments until they get older and acquire more investing experience. He wants you to indicate what you're willing to pay for this product that promises a $15,000 payout 7 years from now. You consider carefully and decide that over the next 7 years you would require a return of 4.5% per year. What price should you tell your friend you'd pay? Your rich aunt sadly just passed, but she left you $10,000. You are hoping to buy a house someday and know that you will need $40,000 to make the down payment on the home. You are perusing investment opportunities and find one offering 9% per year over any maturity (i.e. as long as you like). (a) If you invest the full $10,000 your aunt left you in this opportunity, how long must you wait for it to be sufficiently large to meet your down payment needs? (b) What if you only needed $20,000 for the down payment - how long will you have to wait? In (3) above, why does it take the same amount of time to get from 10k to 20k, as it takes to get from 20k to 40k? You waited just as long, but you increased your "balance" by 10k (from 10k to 20k) in the first "x" years, and you increased your "balance" by 20k (from 20k to 40k) over the second block of "x" years