Find $\bar z$ Of the Center of Mass of the Solid of Given

Multiple Choice

Find $\bar z$ of the center of mass of the solid of given density $\rho ( x , y , z ) = k x \text { bounded }$ by the graphs of the equations $Q : z = 12 - x , z = 0 , y = 0 , y = 4 , x = 0$ .

A) 3
B) 7
C) 6
D) 4
E) 9