21) Find the volume of the solid obtained by rotating the region bounded the given curves about the specific line. Sketch the region, the solid, and a typical disk or washer. a) y = =,y=0x= 1x = 4 about the x - axis b) x = 2 - y', x = y4, about the y - axis 22) Use the method of cylindrical shells to find the volume generated by rotating the region bounded by the given curves about the y-axis. y = 4x - x, y =x 23) Use the method of cylindrical shells to find the volume generated by rotating the region bounded by the given curves about the x-axis. y = x3/2, y = 8, x=0