How long would a Bangladeshi have to work in the U.S. to have the same household impact as a lifetime of microcredit?

According to Lant Pritchett, three weeks. 

But the political system is set up so that everyone has to stay in the country where we drew the boundaries roughly at the end of World War II.  Sooner or later, I think this is gonna go.

Pritchett's book on development through migration: Let Their People Come.