The wheels of a wagon can be approximated as the combination of a thin outer hoop, of radius rh=0.315 m and mass 5.08 kg , and two thin crossed rods of mass 8.23 kg each. A farmer would like to replace his wheels with uniform disks td=0.0651 m thick, made out of a material with a density of 7830 kg per cubic meter. If the new wheel is to have the same moment of inertia about its center as the old wheel about its center, what should the radius of the disk be?