(1) Let x = the measure of each base angle.
(2) Set up an equation and solve for x.
base angle + base angle + 120 degrees = 180 degrees
x + x + 120 degrees = 180 degrees
2x + 120 = 180
2x = 180 - 120
2x = 60
x = 60/2
x = 30
Each base angle of triangle ABC measures 30 degrees.
