How do you factor y= x^2 - 5x + 4 ?

We have, $y = {x}^{2} - 5 x + 4$
$y$=${x}^{2} - 4 x - x + 4$
Or, $y$=$x \left(x - 4\right) - 1 \left(x - 4\right)$
Thus , $y = \left(x - 1\right) \left(x - 4\right)$