(1) Calculate the payback time (in years) for a rooftop solar system if the alternative is purchasing electricity from a utility at a rate $0.12/kWh. Assume the solar system costs $12,000 installed and produces 6,000 kWh per year. The installed costs are offset by a subsidy worth 30% of the total installed cost. The solar system requires $200 per year in annual operating costs. (a) What is the net investment (cost - subsidy)? (4 pts.) (b) What are the annual savings using the rooftop solar compared to purchasing electricity? (4 pts.) (C) What is the payback time? Please provide the answer in units of years. (4 points)