Answer:
3 × 10¹⁹ kg
Step-by-step explanation:
[tex]\text{Mass of water} = 5.9726 \times 10^{ 24}\text{ kg Earth } \times \dfrac{5 \times 10^{-4}\text{ kg water }}{\text{100 kg Earth}} = \mathbf{3 \times 10^{19}}\textbf{ kg water}[/tex]
The answer can have only one significant figure, because you estimated the percent of water to only one significant figure.
