tentukan besar sudut BCA

70° + (180°-(2x+40)°) + (180°-(3x+30)°) = 180°
70° + (180-2x-40)°+(180-3x-30)°=180°
70° + 130°-2x°+140°-3x°=80°
340° - 5x°=180°
5x°=340°-180°
5x°=160°
x°=160°:5°
x°=32°

Sudut BCA = 180°-(3x+30)°
= 180°-(3.32°+30°)
= 180°-(96°+30°)
= 180° - 126°
= 54°