At the beginning of the year, Sheffield Inc. is considering whether to repair and retain an existing machine, or to replace it with a new machine. The following information is available to analyze this decision: Machine overhaul costs (last year) $6700 Repair costs (current year) 3000 Annual operating costs (existing machine) 13500 Annual operating costs (new machine) 8900 Which of the costs being considered for this decision represents a sunk cost?