Multiply $ \dfrac{1}{4} $ by $ 4x-20 $ to get $ \dfrac{ 4x-20 }{ 4 } $.

Step 1: Write $ 4x-20 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{1}{4} \cdot 4x-20 & \xlongequal{\text{Step 1}} \frac{1}{4} \cdot \frac{4x-20}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 1 \cdot \left( 4x-20 \right) }{ 4 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 4x-20 }{ 4 } \end{aligned} $$

Subtract $ \dfrac{4x-20}{4} $ from $ 5x+20 $ to get $ \dfrac{ \color{purple}{ 16x+100 } }{ 4 }$.

Step 1: Write $ 5x+20 $ 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 first fraction by $\color{blue}{ 4 }$.

$$ \begin{aligned} 5x+20- \frac{4x-20}{4} & \xlongequal{\text{Step 1}} \frac{5x+20}{\color{red}{1}} - \frac{4x-20}{4} = \frac{ \left( 5x+20 \right) \cdot \color{blue}{ 4 }}{ 1 \cdot \color{blue}{ 4 }} - \frac{ 4x-20 }{ 4 } = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ 20x+80 } }{ 4 } - \frac{ \color{purple}{ 4x-20 } }{ 4 }=\frac{ \color{purple}{ 20x+80 - \left( 4x-20 \right) } }{ 4 } = \\[1ex] &=\frac{ \color{purple}{ 16x+100 } }{ 4 } \end{aligned} $$

Multiply $ \dfrac{1}{5} $ by $ \dfrac{16x+100}{4} $ to get $ \dfrac{ 16x+100 }{ 20 } $.

Step 1: Multiply numerators and denominators.

Step 2: Simplify numerator and denominator.

$$ \begin{aligned} \frac{1}{5} \cdot \frac{16x+100}{4} & \xlongequal{\text{Step 1}} \frac{ 1 \cdot \left( 16x+100 \right) }{ 5 \cdot 4 } \xlongequal{\text{Step 2}} \frac{ 16x+100 }{ 20 } \end{aligned} $$