A heat exchanger is being installed as part of a plant modernization program. it costs $80,000, including installation, and is expected to reduce the overall plant fuel cost by $20,000 per year. estimates of the useful life of the heat exchanger range from an optimistic 12 years to a pessimistic 4 years. the most likely value is 5 years. assume the heat exchanger has no salvage value at the end of its useful life. determine the mean rate of return.