(parallel cross-sections: "parallel" is a mistake)
The solid with circular bases, and square cross-sections perpendicular to the bases is a cylinder, whose height is equal to the diameter of a base circle.
Check the picture attached.
The radius is 5r, so the height=diameter=10r
Volume(cone)=S(base)*height=[tex] \pi R^{2}*h= \pi (5r)^{2}*10r= \pi *25 *r^{2}*10r=250r ^{3} [/tex] (units cube)
Answer: [tex]250r ^{3} [/tex]
