Final answer:
A low-income homeowner who has installed high-efficiency insulation in their attic in Austin may be eligible for the Weatherization Assistance Program. The other options mentioned in the question are not specific to low-income homeowners or insulation upgrades in the attic.
Step-by-step explanation:
A low-income homeowner who has installed high-efficiency insulation in their attic in Austin may be eligible for the Weatherization Assistance Program. This program provides financial assistance to low-income households to improve energy efficiency in their homes, including insulation upgrades. It is a federal program administered by the Department of Energy.
The other options mentioned in the question, such as the Energy Star tax credit, Federal Solar Investment Tax Credit, and Residential Renewable Energy Tax Credit, are not specific to low-income homeowners or insulation upgrades in the attic. These incentives may be available for other energy-efficient home improvements or renewable energy installations.