a retrofitted​ space-heating system is being considered for a small office building. the system can be purchased and installed for ​$​, and it will save an estimated ​kilowatt-hours (kwh) of electric power each year over a ​-year period. a​ kilowatt-hour of electricity costs ​$​, and the company uses a marr of ​% per year in its economic evaluations of refurbished systems. the market value of the system will be ​$ at the end of ​years, and additional operating and maintenance expenses are ​$ per year. use the​ benefit-cost method to make a recommendation.