The parents of a kindergarten student want to save $260,000 to pay for the estimated cost of her college education. They plan to invest their savings in a mutual fund and based on the past performance of the fund and its projected future performance they estimate that it will give returns that are equivalent to earning about 6.15% interest compounded monthly. How much should the parents deposit at the end of each month into an account paying 6.15% interest compounded monthly so that the account will be worth $260,000 in 18 years?