Factorize each of the following expression:

$x^{2}-11 x y-x+11 y=\left(x^{2}-x\right)+(11 y-11 x y) \quad[$ Regrouping the expressions $]$

$=x(x-1)+11 y(1-x)$      

$=x(x-1)-11 y(x-1)$       $[\because(1-x)=-(x-1)]$

$=(x-11 y)(x-1)$            [Taking out the common factor $(x-1)$ ]