Add $ \dfrac{5}{4} $ and $ \dfrac{3}{2a^2+a-1} $ to get $ \dfrac{ \color{purple}{ 10a^2+5a+7 } }{ 8a^2+4a-4 }$.

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}{ 2a^2+a-1 }$ and the second by $\color{blue}{ 4 }$.

$$ \begin{aligned} \frac{5}{4} + \frac{3}{2a^2+a-1} & = \frac{ 5 \cdot \color{blue}{ \left( 2a^2+a-1 \right) }}{ 4 \cdot \color{blue}{ \left( 2a^2+a-1 \right) }} + \frac{ 3 \cdot \color{blue}{ 4 }}{ \left( 2a^2+a-1 \right) \cdot \color{blue}{ 4 }} = \\[1ex] &=\frac{ \color{purple}{ 10a^2+5a-5 } }{ 8a^2+4a-4 } + \frac{ \color{purple}{ 12 } }{ 8a^2+4a-4 }=\frac{ \color{purple}{ 10a^2+5a+7 } }{ 8a^2+4a-4 } \end{aligned} $$