Supplementary angles are angles that add up to 180 degrees.
180 = 3x + 4 + 8x + 11
Combine like terms.
180 = 11x + 15
Subtract 15 from both sides.
165 = 11x
Divide both sides by 11
15 = x
m<ABC = 3x + 4 = 3(15) + 4 = 45 + 4 = 49 degrees.
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