$$ (-\frac{5}{2})^2 = \frac{ 5 }{ 2 }^{ 2 } \cdot 1 ^ { 2 } = \frac{ 5 }{ 2 }^{ 2 } 1 ^2 = \frac{ 5 }{ 2 }^{ 2 } \lvert 1 \rvert = \frac{25}{4} $$

Multiply $x^4$ by $ \dfrac{25}{4} $ to get $ \dfrac{ 25x^4 }{ 4 } $.

Step 1: Write $ x^4 $ as a fraction by putting $ \color{red}{1} $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} x^4 \cdot \frac{25}{4} & \xlongequal{\text{Step 1}} \frac{x^4}{\color{red}{1}} \cdot \frac{25}{4} \xlongequal{\text{Step 2}} \frac{ x^4 \cdot 25 }{ 1 \cdot 4 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 25x^4 }{ 4 } \end{aligned} $$

Multiply $ \dfrac{25x^4}{4} $ by $ -3+x $ to get $ \dfrac{25x^5-75x^4}{4} $.

Step 1: Write $ -3+x $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{25x^4}{4} \cdot -3+x & \xlongequal{\text{Step 1}} \frac{25x^4}{4} \cdot \frac{-3+x}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 25x^4 \cdot \left( -3+x \right) }{ 4 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ -75x^4+25x^5 }{ 4 } = \frac{25x^5-75x^4}{4} \end{aligned} $$