1. **State the problem:** We need to find the length of the diagonal $x$ of a rectangle with sides 12 inches and 17 inches. 2. **Formula used:** The diagonal $x$ of a rectangle can be found using the Pythagorean theorem: $$x = \sqrt{\text{length}^2 + \text{width}^2}$$ 3. **Apply the formula:** Substitute length = 17 and width = 12: $$x = \sqrt{17^2 + 12^2}$$ 4. **Calculate squares:** $$x = \sqrt{289 + 144}$$ 5. **Add inside the square root:** $$x = \sqrt{433}$$ 6. **Find the square root:** $$x \approx 20.809...$$ 7. **Round to the nearest tenth:** $$x \approx 20.8$$ **Final answer:** The length of the diagonal is approximately **20.8 inches**.