A major renewable energy program is being considered to mitigate the potential impact of climate change. A group of expert estimates that this program will cost $10 billion (in the year 2020 money) to build, and will have an enormous capacity to reduce the level of greenhouse gas emissions. In the absence of this program, the greenhouse gas build-up will impose a real net cost of $85 billion in the year 2100. At what rate of discount will this program become viable? (your answer must be rounded off to the nearest %, i.e., no decimal places)