someone answered this one incorrrectly, please help me solve this question the right way. Show me all the steps

1. A heat exchanger is being installed as part of a plant modernization program. It costs $120,000, including installation, and is expected to reduce the overall plant fuel cost by $24,000 per year. Estimates of the useful life of the heat exchanger range from an optimistic 10 years to a pessimistic 3 years. The most likely value is 5 years. The heat exchanger has no salvage value at the end of its useful life. a. Determine the pessimistic, most likely, and optimistic rates of return. b. Use the beta distribution to compute the mean life. From this mean life, determine the rate of return. You may use Excel to determine the rate of return, but you must submit your work. Alternatively, you may compute it by hand