6. A project constructed in one year is estimated to cost $7.8 million with an economic life of 50 years. Estimates of its earnings are made as follows: What discount rate will give equal benefits and costs? (This may require trial and error.) 7. A local council plans to purchase a new garbage truck. Two models are equally acceptable. Which truck would you recommend they purchase on economic grounds? The expected life of each truck is 5 years with zero salvage value and an interest rate of 7%