1. **State the problem:** We have a dartboard with a diameter of 18 inches. We need to find its radius and circumference. 2. **Recall formulas:** - Radius $r$ is half the diameter: $$r = \frac{d}{2}$$ - Circumference $C$ of a circle is given by: $$C = 2\pi r$$ 3. **Calculate the radius:** $$r = \frac{18}{2} = 9$$ inches 4. **Calculate the circumference:** $$C = 2\pi \times 9 = 18\pi$$ inches 5. **Final answers:** - Radius = 9 inches - Circumference = $18\pi$ inches (approximately 56.55 inches)