Chapter 1 - Expressions, Equations, and Inequalities - 1-4 Solving Equations - Practice and Problem-Solving Exercises - Page 31: 53

smaller angle = $40^o$ larger angle = $140^o$

Let $x$ be the angle and $y$ be its supplement. Then, $20+3x=y$ $x+y=180$ Substitute one equation into the other and simply using algebra: $x+20+3x=180 \\4x+20=180 \\4x=160 x=40$ Substitute the x value into the second equation and solve for y: $40+y=180 \\y=140$