Divide $ \dfrac{x^2}{4} $ by $ x^2 $ to get $ \dfrac{1}{4} $.

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

Step 2: Cancel $ \color{blue}{ x^2 } $ in first and second fraction.

Step 3: Multiply numerators and denominators.

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

Divide $ \dfrac{1}{4} $ by $ 4 $ to get $ \dfrac{1}{16} $.

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

Step 2: Multiply numerators and denominators.

$$ \begin{aligned} \frac{ \frac{1}{4} }{4} = \frac{1}{4} \cdot \frac{\color{blue}{1}}{\color{blue}{4}} = \frac{1}{16} \end{aligned} $$

Subtract $ \dfrac{4}{x} $ from $ \dfrac{1}{16} $ to get $ \dfrac{ \color{purple}{ x-64 } }{ 16x }$.

To subtract 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 $\color{blue}{ 16 }$.

$$ \begin{aligned} \frac{1}{16} - \frac{4}{x} & = \frac{ 1 \cdot \color{blue}{ x }}{ 16 \cdot \color{blue}{ x }} - \frac{ 4 \cdot \color{blue}{ 16 }}{ x \cdot \color{blue}{ 16 }} = \\[1ex] &=\frac{ \color{purple}{ x } }{ 16x } - \frac{ \color{purple}{ 64 } }{ 16x }=\frac{ \color{purple}{ x-64 } }{ 16x } \end{aligned} $$