University of Illinois trustees have voted to freeze in-state tuition rates at the school’s three campuses.  The plan announced last week and unanimously approved by trustees Thursday in Chicago will freeze tuition at $12,036 a year in Urbana-Champaign.  State law guarantees first-year students at public universities their tuition won’t increase for four years.  Tuition will increase by 2 percent for non-Illinois residents.  Tuition at universities across the country has increased sharply in recent years.  Housing costs at the three campuses, though, will increase.  At the Urbana-Champaign campus the increase will be 1.5 percent to $10,332 a year.