If the government of smartypants wanted to subsidize college education, how much would it subsidize each student to achieve the socially optimal level of education?

I think it would depend upon the financial background of a student. A good family financial support does not need a big amount for education. The US offers part time job opportunities that are favorable for them. The percentage should still look into a financial assessment for school education and have a definite clustered support that is based on their capacity to go through the whole course.

Currently, as of february 2016, an american traveling in france would be by the exchange rate. the weakness of the euro and the strength of the us dollar means that items in france cost less to an american than they otherwise would. of course, if this trend reverses and the us dollar weakens and the euro strengthens, such as was happening in early 2008, an american traveling in france would have an adverse experience because items would cost relatively more.