Problem 9: a. Give the formula that should be used to answer the following question. (Do not actually calculate the answer, just give the formula.) Joe invested $8,000 at the end of each month for five years into an account earning 3%/year com- pounded monthly. How much was his account worth at the end of the five year period ? b. Give the formula that should be used to answer the following question. (Do not actually calculate the answer, just give the formula.) Joe invested $8,000 on Jan. 1, 2010 in an account earning 3%/year compounded monthly. How much was his account worth on Dec. 31, 2014? c. If you used the same formula for both questions above, explain why the two questions require the use of the same formula. Similarly, if you used different formulas, explain why the two questions require the use of different formulas