Multiply $3$ by $ \dfrac{x^2}{4} $ to get $ \dfrac{ 3x^2 }{ 4 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

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

Multiply $ \dfrac{3x^2}{4} $ by $ \dfrac{16}{9} $ to get $ \dfrac{ 48x^2 }{ 36 } $.

Step 1: Multiply numerators and denominators.

Step 2: Simplify numerator and denominator.

$$ \begin{aligned} \frac{3x^2}{4} \cdot \frac{16}{9} \xlongequal{\text{Step 1}} \frac{ 3x^2 \cdot 16 }{ 4 \cdot 9 } \xlongequal{\text{Step 2}} \frac{ 48x^2 }{ 36 } \end{aligned} $$

Multiply $ \dfrac{48x^2}{36} $ by $ x $ to get $ \dfrac{ 48x^3 }{ 36 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{48x^2}{36} \cdot x & \xlongequal{\text{Step 1}} \frac{48x^2}{36} \cdot \frac{x}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 48x^2 \cdot x }{ 36 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 48x^3 }{ 36 } \end{aligned} $$

Multiply $ \dfrac{48x^3}{36} $ by $ -3x^2 $ to get $ \dfrac{ -144x^5 }{ 36 } $.

Step 1: Write $ -3x^2 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{48x^3}{36} \cdot -3x^2 & \xlongequal{\text{Step 1}} \frac{48x^3}{36} \cdot \frac{-3x^2}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 48x^3 \cdot \left( -3x^2 \right) }{ 36 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ -144x^5 }{ 36 } \end{aligned} $$