Machine X and Y each sell for 100,000 and each has a life of 20 years. Machine X produces 1500 units per year, has an annual maintenance expense of 1000 and a salvage value of 26,890. Machine Y produces U units per year, has an annual maintenance expense of 1600 and no salvage value. At an effective annual rate of interest of 8%, a buyer is indifferent between the two machines. Determine U.