Answer
$$7.0 \times 10^{20} \space L$$
Work Step by Step
$$1.8 \times 10^8 \space km^2 \times \Bigg(\frac{1000 \space m}{1 \space km} \Bigg)^2 = 1.8 \times 10^{14} \space m^2$$
$$V = 1.8 \times 10^{14} \space m^2 \times 3.9 \times 10^3 \space m =
7.0 \times 10^{17} \space m^3$$
$$7.0 \times 10^{17} \space m^3 \times \frac{1000 \space L}{1 \space m^3} = 7.0 \times 10^{20} \space L$$
