Can someone please help me.
36x^2z-6xyz-6y^2z?
I think you mean this
$\displaystyle 36x^2z-6xyz-6y^2z$
Now come the "trick"
lets add zero to the equation $\displaystyle 0=(12xyz-12xyz)$
$\displaystyle 36x^2z-6xyz-6y^2z+0 \to 36x^2z-6xyz-6y^2z+12xyz-12xyz$
Now rewriting as
$\displaystyle 36x^2z-18xyz+12xyz-6y^2z \iff 18xz(2x-y)+6yz(2x-y)$
$\displaystyle (2x-y)(18xz+6yz)=6(2x-y)(3xz+yz)$