When the survey results came back, employees indicated that the lighting in the building is too low. There are 50 lights in the building. It will cost $50 to replace each light. The new lights are LED lights that are brighter and more efficient and last 10 years. It will save the company $350 per year in energy costs, plus make a brighter more productive work space making employees happier. How many years will it take for the new lights to pay for themselves?