1. **State the problem:** Find the surface area of a sphere with a diameter of 30 miles. 2. **Formula:** The surface area $A$ of a sphere is given by the formula: $$A = 4\pi r^2$$ where $r$ is the radius of the sphere. 3. **Find the radius:** The radius $r$ is half the diameter, so: $$r = \frac{30}{2} = 15 \text{ miles}$$ 4. **Calculate the surface area:** Substitute $r = 15$ into the formula: $$A = 4\pi (15)^2 = 4\pi \times 225 = 900\pi$$ 5. **Final answer:** The surface area is: $$A = 900\pi \approx 2827.43 \text{ square miles}$$ This means the sphere's surface area is approximately 2827.43 square miles.