Mr. Diamond expects to invest $1000 per year for each of the next 20 years in an investment plan that pays 10% per year, compounded annually. At the end of the 20th year, he expects to withdraw the balance in his investment plan and deposit it in a savings account. This savings account pays 6% per year, compounded monthly. Mr. Diamond wants to withdraw a fixed amount from this savings account each month, for a total of five years. How large may this fixed amount be? [answer is given but i need an explanation as to how to get to it]