Complex sentence: The first Federal budget was about $4.6 million and the population in the 1790 U.S. Census was about four million, so that the average federal tax was about $1/person per year.
Split into simpler sentences: The first Federal budget was about $4.6 million and the population in the 1790 U.S. Census was about four million. Hence the average federal tax was about $1/person per year.