Question 587933
I hope we can use the formula {{{V=2pi^2*r^2*R}}} where R is the distance from the center of the torus to the axis of rotation, and r is the radius of a cross section circle (cutting along the axis).
In that case,
{{{(40000pi^2)mm^3=2pi^2(20mm)^2R}}} --> {{{40000mm^3=2*400mm^2*R}}} --> {{{R=40000mm^3/(2*400mm^2)}}} --> {{{highlight(R=50mm)}}}