Hell, you can wipe out poverty in the US for 18 billion.
Mandatory birth control.
Edit: I see a few people have beaten me to to punch here, but it's absolute truth: if you don't have the financial means to support a child, then you shouldn't be having them. Having a social welfare system is a noble and necessary thing, however it has become a means for people to avoid working simply by pumping out children. If you allow yourselve to take a step back, you will notice that just like in any biological sytem, when food (or the means for survival) is plentiful then a population multiplies. Now of course as creatures with a conscience we can't simply abandon people who can't afford to pay their way, but I don't think it's unreasonable to ask those who aren't contributing to society not to increase the burden that they are putting on the rest of us.
I know this is an unpopular view, but it represents the only real solution to the problem (other than that of ensuring compliance to such a program).This comment was edited on Jan 9, 13:08.