1. **State the problem:** We need to find the total surface area of Earth's water, which includes both saltwater and freshwater, and express the answer in scientific notation. 2. **Given data:** - Saltwater surface area = $3.52 \times 10^{8}$ km$^2$ - Freshwater surface area = $9 \times 10^{6}$ km$^2$ 3. **Formula:** Total water surface area = Saltwater surface area + Freshwater surface area 4. **Calculate:** $$3.52 \times 10^{8} + 9 \times 10^{6}$$ 5. **Convert freshwater to the same power of ten:** $$9 \times 10^{6} = 0.09 \times 10^{8}$$ 6. **Add the values:** $$3.52 \times 10^{8} + 0.09 \times 10^{8} = (3.52 + 0.09) \times 10^{8} = 3.61 \times 10^{8}$$ 7. **Final answer:** The total surface area covered by water on Earth is $3.61 \times 10^{8}$ km$^2$. This matches the first option provided.