How do you factor by grouping 9x^2 + 3xy + 3x + y?

$9 {x}^{2} + 3 x y + 3 x + y$
$= \left(9 {x}^{2} + 3 x y\right) + \left(3 x + y\right)$
$= 3 x \left(3 x + y\right) + \left(3 x + y\right)$
$= \left(3 x + 1\right) \left(3 x + y\right)$