Integrate the function upper f (x comma y comma z )equals 6 zf(x, y,z)=6z over the portion of the plane x plus y plus z equals 2x+y+z=2 that lies above the square 0 less than or equals x less than or equals 10≤x≤1, 0 less than or equals y less than or equals 10≤y≤1 in the xy-plane.