1. **State the problem:** We have a triangle with sides 10 cm, 13 cm, and 5 cm, and angles 40°, 90°, and $x^\circ$. We need to find the value of $x$ to 1 decimal place. 2. **Identify the triangle type and known values:** The triangle has a right angle (90°) adjacent to the 5 cm side, and an angle of 40° opposite the 13 cm side. 3. **Use the fact that the sum of angles in a triangle is 180°:** $$x + 40 + 90 = 180$$ 4. **Calculate $x$:** $$x = 180 - 90 - 40$$ $$x = 50$$ 5. **Answer:** The value of $x$ is $50.0^\circ$ to 1 decimal place.