Joe and his sister Patty are considering investing $6,000 to start a used book business. They expect to receive cash inflows of $1,000 each year for the next four years from the business. At the end of the fourth year, they expect to be able to sell the business for $10,000 cash. What is the net present value of the book business investment if Joe and Patty want to earn at least a 12% return from it? (Ignore taxes)