To factor $ 8ax^2-3by+12axy-2bx $ we can use factoring by grouping.
Group $ \color{blue}{ 8ax^2 }$ with $ \color{blue}{ -3by }$ and $ \color{red}{ 12axy }$ with $ \color{red}{ -2bx }$ then factor each group.
$$ \begin{aligned} 8ax^2-3by+12axy-2bx &= ( \color{blue}{ 8ax^2+12axy } ) + ( \color{red}{ -3by-2bx }) = \\ &= \color{blue}{ 4ax( 2x+3y )} \color{red}{ -b( 3y+2x ) } = \\ &= (4ax-b)(2x+3y) \end{aligned} $$