From the following figure find x + y + z.

According to the concept,

considering triangle ACD, y + \({110}^\circ\) = \({120}^\circ\)

⇒ y = \({10}^\circ\)

Considering triangle ABC, the sum of two interior angles of a triangle is equal to the exterior angle of the third angle.

hence, x + z = \({110}^\circ\)

Now, x + y + z

⇒ \({110}^\circ\) + \({10}^\circ\) = \({120}^\circ\)

Therefore, the measure of x + y + z is \({120}^\circ\).