Divide $ \dfrac{35}{256} $ by $ 21 $ to get $ \dfrac{5}{768} $.

Step 1: To divide rational expressions, multiply the first fraction by the reciprocal of the second fraction.

Step 2: Multiply numerators and denominators.

Step 3: Cancel down by $ \color{blue}{7} $

$$ \begin{aligned} \frac{ \frac{35}{256} }{21} & \xlongequal{\text{Step 1}} \frac{35}{256} \cdot \frac{\color{blue}{1}}{\color{blue}{21}} \xlongequal{\text{Step 2}} \frac{35 : \color{blue}{7}}{5376 : \color{blue}{7}} = \\[1ex] &= \frac{5}{768} \end{aligned} $$

Divide $ \dfrac{5}{768} $ by $ 4 $ to get $ \dfrac{5}{3072} $.

To divide rational expressions, multiply the first fraction by the reciprocal of the second fraction.

Step 2: Multiply numerators and denominators.

$$ \begin{aligned} \frac{ \frac{5}{768} }{4} & = \frac{5}{768} \cdot \frac{\color{blue}{1}}{\color{blue}{4}} = \frac{5}{3072} \end{aligned} $$

Multiply $ \dfrac{5}{3072} $ by $ x $ to get $ \dfrac{ 5x }{ 3072 } $.

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.

$$ \begin{aligned} \frac{5}{3072} \cdot x & \xlongequal{\text{Step 1}} \frac{5}{3072} \cdot \frac{x}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 5 \cdot x }{ 3072 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 5x }{ 3072 } \end{aligned} $$