Question 696965
A square, which is flat, doesn't have a volume. 
I think you mean a cube. The equation for
the volume of a cube is:
{{{ V = s^3 }}} where {{{ s }}} is a side of the cube
given:
{{{ V = 5625 }}} km3
{{{ 5625 = 17.784^3 }}}
A side of the cube is 17.784 km