Add $ \dfrac{5}{2x^2} $ and $ \dfrac{x}{5} $ to get $ \dfrac{ \color{purple}{ 2x^3+25 } }{ 10x^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}{ 5 }$ and the second by $\color{blue}{ 2x^2 }$.

$$ \begin{aligned} \frac{5}{2x^2} + \frac{x}{5} & = \frac{ 5 \cdot \color{blue}{ 5 }}{ 2x^2 \cdot \color{blue}{ 5 }} + \frac{ x \cdot \color{blue}{ 2x^2 }}{ 5 \cdot \color{blue}{ 2x^2 }} = \\[1ex] &=\frac{ \color{purple}{ 25 } }{ 10x^2 } + \frac{ \color{purple}{ 2x^3 } }{ 10x^2 }=\frac{ \color{purple}{ 2x^3+25 } }{ 10x^2 } \end{aligned} $$