a, \(3x^2-6xyz+3y^2z=3\left(x^2-2xyz+y^2z\right)\)
b, \(x^2-3x-y^2+3y=x^2-y^2-3x+3y=\left(x-y\right)\left(x+y\right)-3\left(x-y\right)\)
\(=\left(x-y\right)\left(x+y+3\right)\)
c, \(3x^2-11x+6=3x^2-9x-2x+6x\)
\(=x\left(3x-2\right)-3\left(3x-2\right)=\left(x-3\right)\left(3x-2\right)\)