Add $ \dfrac{-4}{x-1} $ and $ \dfrac{3-x}{x} $ to get $ \dfrac{ \color{purple}{ -x^2-3 } }{ x^2-x }$.

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 $\color{blue}{ x-1 }$.

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