Answer:
∠A = 80°
Step-by-step explanation:
The left vertex of the triangle = 4x - 3 ( vertical angles )
The external angle of a triangle is equal to the sum of the 2 opposite interior angles.
125° is an external angle of the triangle, thus
5x + 20 + 4x - 3 = 125, that is
9x + 17 = 125 ( subtract 17 from both sides )
9x = 108 ( divide both sides by 9 )
x = 12
Hence
∠A = 5x + 20 = (5 × 12) + 20 = 60 + 20 = 80°
