Find the volume of the following solids. The base of a solid is the region bounded by the graphs of y = 6x, y = 12, and x =0. The cross-sections perpendicular to the x-axis are a. rectangles of height 12. b. rectangles of perimeter 60. a. V= 144 (Type an exact answer, using radicals as needed.) b. V = (Type an exact answer, using radicals as needed.)