To factor $ 2xy-4bx+3by-6b^2 $ we can use factoring by grouping.
Group $ \color{blue}{ 2xy }$ with $ \color{blue}{ -4bx }$ and $ \color{red}{ 3by }$ with $ \color{red}{ -6b^2 }$ then factor each group.
$$ \begin{aligned} 2xy-4bx+3by-6b^2 &= ( \color{blue}{ 2xy-4bx } ) + ( \color{red}{ 3by-6b^2 }) = \\ &= \color{blue}{ 2x( y-2b )} + \color{red}{ 3b( y-2b ) } = \\ &= (2x+3b)(y-2b) \end{aligned} $$