Add $x$ and $ \dfrac{5}{4x^2} $ to get $ \dfrac{ \color{purple}{ 4x^3+5 } }{ 4x^2 }$.

Step 1: Write $ x $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: To add raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $\color{blue}{ 4x^2 }$.

$$ \begin{aligned} x+ \frac{5}{4x^2} & \xlongequal{\text{Step 1}} \frac{x}{\color{red}{1}} + \frac{5}{4x^2} = \frac{ x \cdot \color{blue}{ 4x^2 }}{ 1 \cdot \color{blue}{ 4x^2 }} + \frac{ 5 }{ 4x^2 } = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ 4x^3 } }{ 4x^2 } + \frac{ \color{purple}{ 5 } }{ 4x^2 }=\frac{ \color{purple}{ 4x^3+5 } }{ 4x^2 } \end{aligned} $$