The U.S. Department of Energy estimates that up to 10 percent of the energy use of a house can be saved by caulking and weather stripping doors and windows to reduce air leaks at a cost of about $50 for materials for an average home with 12 windows and 2 doors. Caulking and weather-stripping every gas-heated home properly would save enough energy to heat about 4 million homes. The savings can be increased by installing storm windows. Determine how long it will take for the caulking and weather-stripping to pay for itself from the energy they save for a house whose annual energy use is $1100.