4.7 An irrigation return flow drain has sampling equipment that can be powered by solar cells or by running an electric line to the site and using conventional power. Solar cells will cost $14,000 to install with a useful life of 10 years. Annual costs for inspection, cleaning are expected to be $1500. A new power line will cost $12,000 to in stall and the power costs are estimated at $600 per year. The salvage value of the solar cells is expected to be 25% of the first cost when the sampling project ends in 4 years. The electric line will stay in place, so its salvage value is considered to be zero. At an interest rate of 10% per year, which alternative should be selected? 4.10 The costs associated with manufacturing a multi function portable gas analyzer are estimated. At an interest rate of 8% per year and a present worth analysis, which method should be selected? Manual Robotic First cost. $ -425,000 -850,000 M&O cost, year 1, $ -90,000 -10,000 Increase in M&O, $/year 7,000 1,000 Salvage value, $ 80,000 300,000 Life, years 5 5 4.13 An undergraduate engineering student and her husband operate a pet-sitting service to help make ends meet. They want to add a daily service of a photo places online for pet owners who are traveling. The estimates are: equipment and setup cost $950; net monthly income over costs $70. Over a period of 3 years, will the service make at least 12% per year compounded monthly