21. Very good on the numbers, the last bit has to come from cuts on other programs.
Social Security is still pretty much self contained as it is and won't be a problem for another 15 or 20 years. No cuts are are needed there. When cuts are needed, they will be structured as lower payments based on funds available after the trust fund is exhausted.
Nobody wants to touch Medicare or Medicaid.
All that really leaves are the non-defense discretionary spending departments to cut, which Obama promised to freeze but didn't. Funding for these departments was about $660 billion for FY 2010. All the various departments are funded through this portion and would be cut. This includes the EPA, Education, Health and Human Services, among the many other departments.
I have heard some say to cut defense completely, which would be very bad for the US and world. History and the corporate greed everyone hates show that human nature is sometimes rather nasty. Most people are fairly good, but they are not the ones that lust for power and obtain the leadership positions. The dollar and our economy rests on the shoulders of those who put on a uniform and protect our freedom. It is tied to our military might and ability to maintain freedom of trade across the world. Even the countries that don't like us benefit from this.
At this point, I think most people are living in a fairy tale land. We have to make a lot of hard cuts to programs and increase taxes to balance the budget. It is not going to be fun or easy, but it has to be done one way or another.