Let R be the region bounded by the following curves. Find the volume of the solid generated when R is revolved about the​ y-axis. ​, ​, A coordinate system has an unlabeled x-axis and a vertical y-axis labeled from less than 0 to 21 plus. From left to right, a line labeled y equals x starts at (0, 0) and rises in quadrant 1. From left to right, a second line labeled y equals 7 x starts at (0, 0) and rises at a steeper rate in quadrant 1. A horizontal line segment extends from the second line to the first line at y equals 21. The region above the first line, below the second line, and below the horizontal line segment is shaded and labeled R. A curved arrow is rotated about the y-axis. y=x, y=7x, y=21