Suppose that you earn $1,000 in year 1 and will earn $648 in year 2. If you borrow money against your future income you will have and additional $450 to spend in year 1, and if you lend all of your current income you will have and additional $1,440 to spend in year 2. In both years you consume only food which costs $1 per kilogram in each year.

What is the interest rate that you borrow and lend at?