A U.S. Department of Energy study estimated that LED light bulbs for "typical parking-lot lights at a Walmart in Kansas" over ten years was worth the higher initial investment in the bulbs of $146,800 versus $103,490 for standard bulbs." How could this be worth it? Because in addition to the energy cost savings, LED lights only have to be changed once every 4 or 5 years, while the standard bulbs have to be changed seven times a year. Every light bulb change costs about $50 in labor time. Based on the information above, and assuming no labor cost savings, at least how much would the discounted value of energy savings need to be to make it worth the higher upfront cost of investing in LED bulbs? a. b. Write an equation to show how you would calculate the discounted energy cost savings for a parking lot bulb over ten years. For simplicity, assume the store pays an annual at the end of cach year based on the amount of energy actually used