Suppose you have a personal real rate of return of 4.5% and can purchase an acre of land that is expected to yield an annual constant real net return of $70. You wish to finance the purchase of this land under a 10 year loan but the bank requires that your cash flows cover the entire annual loan payment immediately. If you purchase the land for the highest price you'd be willing to pay and the nominal market interest rate is 7%, how big of a down payment do you need to make to purchase this land?