Light-emitting diode (LED) IIght bulbs have become requilred In recent years, but do they make financlal sense? Suppose a typical 60 -watt Incandescent light bulb costs $.45 and lasts for 1,000 hours. A 7-watt LED, which provides the same light, costs $2.25 and lasts for 40,000 hours. A kilowatt-hour of electricity costs $.121, which is about the national average. A kllowatt-hour is 1,000 watts for 1 hour. Suppose you have a residence with a lot of Incandescent bulbs that are used on average 500 hours a year. The average bulb Will be about halfway through its life, so it will have 500 hours remaining (and you can't tell which bulbs are older or newer). If you require a 10 percent return, at what cost per kllowatt-hour does it make sense to replace your incandescent bulbs today? (A negatlve answer should be Indlcated by a minus sign. Do not round Intermedlate calculatlons and round your answer to 6 decimal places, e.g., 32.161616.)