If you’re Bill Gates, the answer came last week when the Gates Foundation released its annual letter. Front and center is the world’s quest to end polio. This is a big deal. Since 2005 Gates has spent $1.3 billion on polio eradication, and the world as a whole has spent $9 billion since 1988. In that timeframe, polio cases have dropped from 350,000 a year to under 1,500 in 2010.