7PM This episode's headline: Treasury's Taxes: Making it Simple; Schroeder Update; 55 MPH: Lives vs. Dollars?. The guests include In Houston: Sen. LLOYD BENTSEN, Democrat, Texas; In Washington: Sen. WILLIAM ARMSTRONG, Republican, Colorado; RICHARD RAHN, U.S. Chambers of Commerce; R. T. McNAMAR, Deputy Secretary of Treasury; JAMES BAXTER, Citizens Coalition for Rational Traffic Laws; In New York: Gov. RICHARD SNELLING, Republican, Vermont; ALAN ALTSHULER, National Research Council; Reports from NewsHour Correspondents: KWAME HOLMAN, in Louisville. Byline: In New York: ROBERT MacNEIL, Executive Editor; CHARLAYNE HUNTER-GAULT, Correspondent; In Washington: JIM LEHRER, Associate Editor