A Lamina Occupies the Part of the Disk $x ^ { 2 } + y ^ { 2 } \leq 81$

Short Answer

A lamina occupies the part of the disk $x ^ { 2 } + y ^ { 2 } \leq 81$ in the first quadrant. Find its center of mass if the density at any point is proportional to its distance from the x-axis.