Add $ \dfrac{8}{7v-6} $ and $ \dfrac{4}{3v^2} $ to get $ \dfrac{ \color{purple}{ 24v^2+28v-24 } }{ 21v^3-18v^2 }$.

To add raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $ \color{blue}{ 3v^2 }$ and the second by $\color{blue}{ 7v-6 }$.

$$ \begin{aligned} \frac{8}{7v-6} + \frac{4}{3v^2} & = \frac{ 8 \cdot \color{blue}{ 3v^2 }}{ \left( 7v-6 \right) \cdot \color{blue}{ 3v^2 }} + \frac{ 4 \cdot \color{blue}{ \left( 7v-6 \right) }}{ 3v^2 \cdot \color{blue}{ \left( 7v-6 \right) }} = \\[1ex] &=\frac{ \color{purple}{ 24v^2 } }{ 21v^3-18v^2 } + \frac{ \color{purple}{ 28v-24 } }{ 21v^3-18v^2 }=\frac{ \color{purple}{ 24v^2+28v-24 } }{ 21v^3-18v^2 } \end{aligned} $$