Solve the Problem $z = \frac { 1 } { 2 } \sqrt { x ^ { 2 } + y ^ { 2 } }$

Solve the problem.
-Find the centroid of the region enclosed between the cone with equation $z = \frac { 1 } { 2 } \sqrt { x ^ { 2 } + y ^ { 2 } }$ and the plane with equation $z = 3$ .

A) $( \bar { x } , \bar { y } , \bar { z } ) = \left( 0,0 , \frac { 12 } { 5 } \right)$
B) $( \overline { \mathrm { x } } , \overline { \mathrm { y } } , \overline { \mathrm { z } } ) = ( 0,0,2 )$
C) $( \bar { x } , \bar { y } , \bar { z } ) = \left( 0,0 , \frac { 9 } { 4 } \right)$
D) $( \bar { x } , \bar { y } , \bar { z } ) = \left( 0,0 , \frac { 15 } { 8 } \right)$