1. **State the problem:** We need to find the area of a semicircle with diameter $d = 24$ kilometers. 2. **Recall the formula:** The area of a full circle is given by $$A = \pi r^2$$ where $r$ is the radius. 3. **Important rule:** The radius $r$ is half the diameter, so $$r = \frac{d}{2}$$. 4. **Calculate the radius:** $$r = \frac{24}{2} = 12$$ kilometers. 5. **Calculate the area of the full circle:** $$A = \pi \times 12^2 = \pi \times 144 = 144\pi$$ square kilometers. 6. **Calculate the area of the semicircle:** Since a semicircle is half of a circle, $$A_{semicircle} = \frac{1}{2} \times 144\pi = 72\pi$$ square kilometers. 7. **Approximate the value:** Using $\pi \approx 3.1416$, $$A_{semicircle} \approx 72 \times 3.1416 = 226.1952$$ square kilometers. 8. **Round to the nearest hundredth:** $$226.20$$ square kilometers. **Final answer:** The area of the semicircle is approximately $226.20$ square kilometers.