Code AA is for contributions to Roth retirement plan. Box DD is for the cost of your health insurance premiums. These two numbers would NEVER be netted out. If you are working on the health care section,. you would use ONLY the DD amount. If you are working on something related to retirement plan contributions, or the Retirement Savings credit, use ONLY the AA amount. The question means you would only total related amounts from Box 12, such as two different retirement contributions, not two completely unrelated amounts.