Solve the Problem $\mathrm { P } ( \mathrm { x } , \mathrm { y } )$

Multiple Choice

Solve the problem.
-Find the average distance from a point $\mathrm { P } ( \mathrm { x } , \mathrm { y } )$ in the first quadrant of the disk $\mathrm { x } ^ { 2 } + \mathrm { y } ^ { 2 } \leq 81$ to the origin.

A) 3
B) $\frac { 9 } { 2 }$
C) 6
D) $\frac { 9 } { 4 }$