Machine X has an initial cost of dollar 10,000, annual maintenance of dollar 500 per year, and no salvage value at the end of its 4-year useful life. Machine Y costs dollar 20,000. The last year there is no maintenance cost. The second year, maintenance is dollar 100, and it increases dollar 100 per year in subsequent years. The machine has an anticipated dollar 5000 salvage value at the end of its 12-year useful life. If interest is 8%, which machine should be selected? (use PW method)