ANSWER:
The volume is 16.36 cubic kilometers
STEP-BY-STEP EXPLANATION:
We have the formula to calculate the volume of the figure would be:
[tex]V=A_b\cdot h[/tex]The height is known to be 2 km, we must calculate the area of the base, which is a triangle and we can calculate it as follows:
[tex]\begin{gathered} A_b=\sqrt[]{s\cdot(s-a)\cdot(s-b)\cdot(s-c)} \\ \text{where s is the semiperimeter } \\ s=\frac{p}{2} \\ p=4+5+8 \\ p=17 \\ \text{replacing} \\ s=\frac{17}{2}=8.5 \\ \text{ now, replacing in the area} \\ A_b=\sqrt{8.5\cdot\left(8.5-4\right)\cdot\left(8.5-5\right)\cdot\left(8.5-8\right)} \\ A_b=8.18 \end{gathered}[/tex]Now, replacing in the volume:
[tex]\begin{gathered} V=\text{8}.18\cdot2 \\ V=16.36 \end{gathered}[/tex]