Final answer:
The total surface area of Earth covered by water is the sum of the saltwater and freshwater surface areas, resulting in 4.613 x 10^8 km².
Step-by-step explanation:
The approximate total surface area of Earth is 5.1 x 10^8 km^2. This includes both land and water. The surface area of all the salt water on Earth is approximately 352,000,000 km^2, and the surface area of all the freshwater on Earth is approximately 9 x 10^6 km^2. To find out how much of Earth's surface is covered in water, we add the surface areas of salt water and freshwater together: 352,000,000 km^2 + 9 x 10^6 km^2 = 3.61 x 10^8 km^2. Therefore, approximately 3.61 x 10^8 km^2, or option a., of Earth's surface is covered in water.
To calculate the total surface area of Earth covered by water, including both salt and freshwater, we add the surface area of salt water, which is 352,000,000 km², to that of freshwater, which is 9 x 10⁶ km². Performing the addition in scientific notation:
Surface area of salt water = 3.52 x 10⁸ km² (Given in standard form)
Surface area of freshwater = 9 x 10⁶ km² (Given in scientific notation)
Total water cover = 3.52 x 10⁸ km² + 0.09 x 10⁸ km²
= (3.52 + 0.09) x 10⁸ km²
= 3.61 x 10⁸ km²
Hence, the correct answer is c. 4.613 x 10⁸ km².