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For a particular replacement study, Mark calculated the marginal costs of the defender and a challenger. Part a: (10 points) The marginal costs for a challenger in EOYs 1, 2, and 3 are $12,000, $9,000, and $11,000 respectively. If the interest rate is 10%, assist Mark in calculating EUAC (for each of the three years) for the challenger. Part b: (3 points) What is the economic life of the challenger? Part c: (5 points) If the EUACs of the defender for the next three years are $10,500, $9,785, and $9850, respectively, should Mark replace the defender with the challenger? If yes, when