Answer:
see explanation
Step-by-step explanation:
The exterior angle of a triangle is equal to the sum of the 2 opposite interior angles.
∠ CBD is an exterior angle of the triangle, then
6x = x + 40 + 3x + 10, that is
6x = 4x + 50 ( subtract 4x from both sides )
2x = 50 ( divide both sides by 2 )
x = 25
Thus
∠ CBD = 6x = 6 × 25 = 150°
∠ CBA and ∠ CBD are adjacent angles and supplementary, sum to 180°, then
150° + ∠ CBA = 180° ( subtract 150° from both sides )
∠ CBA = 30°
