Given that a mountain is in the shape of a cone, the figure is shown below
Since the mountain have the shape of a cone, we use the volume of a cone to find the volume of the mountain
The formula for the volume, V, of a cone is

Given that
![\begin{gathered} h=5.4\operatorname{km} \\ r=3\operatorname{km} \end{gathered}]()
Substitute the values into the formula for the volume of a mountain
![\begin{gathered} V=(1)/(3)\pi r^2h \\ V=(1)/(3)*\pi*3^2*5.4=50.8938\approx51\operatorname{km}^3\text{ (nearest whole number)} \\ V=51\operatorname{km}\text{ (nearest whole number)} \end{gathered}]()
Hence, the volume, V, of the mountain is 51km³ (nearest whole number)