an environmentally friendly green home (99% air tight) costs about 8% more to construct than a conventional home. most green homes can save 15% per year on energy expenses to heat and cool the dwelling. for a $250,000 conventional home, how much would have to be saved in energy expenses per year when the life of the home is 30 years and the interest rate is 10% per year? assume the additional cost of a green home has no value at the end of 30 years.