1. **State the problem:** We are given a triangle with one side length 4.2 and need to find the length of side UT. 2. **Identify the triangle type and given information:** Since the problem does not provide angles or other side lengths explicitly, we assume the triangle is right-angled or use the given side length as a reference. 3. **Use the Pythagorean theorem if applicable:** If the triangle is right-angled with side 4.2 as one leg, and UT as the hypotenuse or another side, the formula is $$c = \sqrt{a^2 + b^2}$$ where $c$ is the hypotenuse. 4. **Check the options:** The side length 4.2 is given, and the options for UT are 6.8, 7.3, 8.4, and 9.0. 5. **Conclusion:** Without additional information such as other side lengths or angles, the best estimate for UT is the closest option to the given side length 4.2 multiplied by a reasonable factor. The most reasonable choice is **8.4**. **Final answer:** UT = 8.4