Besar A. 50 derajat B. 60 derajat C. 70 derajat D. 80 derajat

BAC + ACB = 4x - 10°
60° + 2x = 4x - 10°
60° + 10° = 4x - 2x
70° = 2x
35° = x

60° + (2x) + ABC = 180°
60° + (2.35) + ABC = 180°
60 + 70 + ABC = 180
130° + ABC = 180
ABC = 180° - 130°
ABC = 50°(a)