3. A more energy efficient air conditioner costs $5000. It will save 10% a year on electricity. Its expected useful life is 20 years. The discount rate is 3% a year. The expected cost of electricity each year is as follows: Time Cost of electricity 1-3 $4000 4-8 $4500 9-20 $3000 Determine the payback, IRR, and NPV for the air conditioner