Subtract $ \dfrac{8}{12x-8} $ from $ \dfrac{7}{3} $ to get $ \dfrac{ \color{purple}{ 84x-80 } }{ 36x-24 }$.

To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $ \color{blue}{ 12x-8 }$ and the second by $\color{blue}{ 3 }$.

$$ \begin{aligned} \frac{7}{3} - \frac{8}{12x-8} & = \frac{ 7 \cdot \color{blue}{ \left( 12x-8 \right) }}{ 3 \cdot \color{blue}{ \left( 12x-8 \right) }} - \frac{ 8 \cdot \color{blue}{ 3 }}{ \left( 12x-8 \right) \cdot \color{blue}{ 3 }} = \\[1ex] &=\frac{ \color{purple}{ 84x-56 } }{ 36x-24 } - \frac{ \color{purple}{ 24 } }{ 36x-24 }=\frac{ \color{purple}{ 84x-80 } }{ 36x-24 } \end{aligned} $$