Multiply $9$ by $ \dfrac{x^2}{36} $ to get $ \dfrac{ 9x^2 }{ 36 } $.

Step 1: Write $ 9 $ as a fraction by putting $ \color{red}{1} $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} 9 \cdot \frac{x^2}{36} & \xlongequal{\text{Step 1}} \frac{9}{\color{red}{1}} \cdot \frac{x^2}{36} \xlongequal{\text{Step 2}} \frac{ 9 \cdot x^2 }{ 1 \cdot 36 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 9x^2 }{ 36 } \end{aligned} $$

Multiply $ \dfrac{9x^2}{36} $ by $ x^2 $ to get $ \dfrac{ 9x^4 }{ 36 } $.

Step 1: Write $ x^2 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{9x^2}{36} \cdot x^2 & \xlongequal{\text{Step 1}} \frac{9x^2}{36} \cdot \frac{x^2}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 9x^2 \cdot x^2 }{ 36 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 9x^4 }{ 36 } \end{aligned} $$

Subtract $180x$ from $ \dfrac{9x^4}{36} $ to get $ \dfrac{ \color{purple}{ 9x^4-6480x } }{ 36 }$.

Step 1: Write $ 180x $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the second fraction by $\color{blue}{36}$.

$$ \begin{aligned} \frac{9x^4}{36} -180x & \xlongequal{\text{Step 1}} \frac{9x^4}{36} - \frac{180x}{\color{red}{1}} = \frac{ 9x^4 }{ 36 } - \frac{ 180x \cdot \color{blue}{ 36 }}{ 1 \cdot \color{blue}{ 36 }} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ 9x^4 } }{ 36 } - \frac{ \color{purple}{ 6480x } }{ 36 }=\frac{ \color{purple}{ 9x^4-6480x } }{ 36 } \end{aligned} $$