To factor $ 6ax^2-9ax-4cx+6c $ we can use factoring by grouping.
Group $ \color{blue}{ 6ax^2 }$ with $ \color{blue}{ -9ax }$ and $ \color{red}{ -4cx }$ with $ \color{red}{ 6c }$ then factor each group.
$$ \begin{aligned} 6ax^2-9ax-4cx+6c &= ( \color{blue}{ 6ax^2-9ax } ) + ( \color{red}{ -4cx+6c }) = \\ &= \color{blue}{ 3ax( 2x-3 )} \color{red}{ -2c( 2x-3 ) } = \\ &= (3ax-2c)(2x-3) \end{aligned} $$