1. **State the problem:** We have a triangle with angles 115°, 35°, and an unknown angle $x$. We need to find $x$. 2. **Formula used:** The sum of the interior angles of any triangle is always 180°. This means: $$115^\circ + 35^\circ + x = 180^\circ$$ 3. **Calculate $x$:** $$x = 180^\circ - 115^\circ - 35^\circ$$ 4. **Simplify:** $$x = 180^\circ - 150^\circ = 30^\circ$$ 5. **Answer:** The unknown angle $x$ is $30^\circ$. This works because the angles in a triangle must add up to 180°, so subtracting the known angles from 180° gives the missing angle.