Let R be the region bounded by the following curves. Use the shell method to nd the volume of the solid generated when R is revolved about the xaxis. y=21 -x.y=x, and y=0 Set up the integral that gives the volume of the solid, Use increasing limits of integration. Select the correct choice below and ll in the answer boxes to complete your choice. (Type an exact answer.) The volume is E. (Type an exact answer.)