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a. If you invest $300 per month at the beginning of each month for the next 20 years into an account earning 5% annually, how much will you have in exactly 20 years?
b. If at the end of the ten years in part a above you increase your monthly payment to $450 per month, what will be the total value of the account after another ten years has gone by (i.e., at the end of 20 years)? How much of this total value represents the contributed principal, and how much is interest?