4. (25 points) You deposit $C into an account at the end of each 4-year period for 40 years. The account credits interest at an annual effective interest rate of i. The accumulated amount in the account at the end of 40 years is 5 times the accumulated amount in the account at the end of 20 years. Find the value of i. 5. (25 points) The used price of a specific car model depreciates relative to the new price according to the annual discount rates in the table below. If you only have half of the new car price available right now, what is the lowest age used car you can afford? (Hint: the used car you can afford is older than 4yrs.) Age Discount Date 1 15% 2 10% 3 5% 4+ 3%