To the best of my knowledge, my university salary is paid out of what the university calls the "general fund". That fund includes the money the university gets from tuition, the money it gets from the state (except possibly for state money earmarked for specific projects, like a new building), and I think also the indirect cost funds from research grants (and maybe other income sources too). Once that money is in the general fund, it gets completely mixed together, regardless of source. And I get the same salary, entirely from that fund, whether I'm teaching my normal course load or whether part of my time is devoted to administrative duties, or whether I'm on sabbatical. So, as far as I can tell, the proportion of my salary that comes from tuition is just the proportion of the general fund that comes from tuition; no finer analysis is possible. (Unfortunately, I don't know what proportion of the general fund comes from tuition, but, since the University of Michigan is a public institution, that information is undoubtedly publicly available somewhere. I heard a figure of 25%) [Edit: Deleted the sentence about "25% quite some years ago, but not from an authoritative sourcesource".) That 25% was for state support, which has probably decreased since then. Tuition is probably a much larger share of the general fund.]
