problem: Susan Robinson is planning for her retirement. She is thirty years old today and would like to have 600,000 dollars when she turns 55. She estimates that she will be able to earn a nine percent rate of return on her retirement investments over time; she wants to set aside a constant amount of money every year [at the end of the year] to help achieve her objectives. How much money must Robinson invest at the end of each of the next twenty-five years to realize her goal of 600,000 dollars at the end of that time?