1. The problem states: The circumference of a circle is 21 cm. We need to find the diameter of the circle, rounded to 1 decimal place. 2. Recall the formula for the circumference of a circle: $$C = \pi d$$ where $C$ is the circumference and $d$ is the diameter. 3. We can rearrange the formula to solve for the diameter: $$d = \frac{C}{\pi}$$ 4. Substitute the given circumference $C = 21$ cm into the formula: $$d = \frac{21}{\pi}$$ 5. Calculate the value using $\pi \approx 3.1416$: $$d = \frac{21}{3.1416} \approx 6.685$$ 6. Round the diameter to 1 decimal place: $$d \approx 6.7 \text{ cm}$$ Therefore, the diameter of the circle is approximately 6.7 cm.