calc prob..someone help

<p>ok its a difference equation prob... and here it is..dun dun dun!</p>

<p>Mary wants to take out a loan. She can afford to make monthly payments of 400 dollars and wants to pay the loan off after exactly 20 years.
What is the maximum amount that Mary can afford to borrow if the bank charges interest at an annual rate of 6 percent, compounded monthly?</p>