1. **Problem:** Find the missing angle $x$ in the triangle with angles 39°, $x$, and 49°. 2. **Formula:** The sum of interior angles in a triangle is always 180°. $$\text{Sum of angles} = 180^\circ$$ 3. **Apply the formula:** $$39^\circ + x + 49^\circ = 180^\circ$$ 4. **Simplify:** $$88^\circ + x = 180^\circ$$ 5. **Isolate $x$:** $$x = 180^\circ - 88^\circ$$ 6. **Calculate:** $$x = 92^\circ$$ 7. **Answer:** The missing angle $x$ is $92^\circ$. This uses the fundamental property of triangles that their interior angles sum to 180°, allowing us to find the unknown angle by subtracting the known angles from 180°.