Besar sudut ABC adalah...

(3X-40) + (X+84) = 180
4X+44 = 180
4X = 136
X = 34

sudut ACB = 3X-40
3.34-40
102-40
62

sudut ABC = 180-(54+62) = 64°

(3x - 40) + (x + 84) = 180 
4x = 136
x = 34

besar ∠ACB = 62°

∠ABC = 180 - (54 + 62) = 64°