1. **State the problem:** We are given a triangle with interior angles 40° and 80°, and an exterior angle adjacent to the triangle labeled $x^\circ$. We need to find the value of $x$. 2. **Recall the exterior angle theorem:** The exterior angle of a triangle is equal to the sum of the two opposite interior angles. 3. **Apply the theorem:** The exterior angle $x$ is adjacent to the interior angle at the bottom right vertex. The two opposite interior angles are 40° and 80°. 4. **Calculate $x$:** $$ x = 40 + 80 = 120 $$ 5. **Conclusion:** The value of the exterior angle $x$ is 120°.