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

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}{ x }$ and the second by $\color{blue}{ x^2 }$.

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