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

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.

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

Multiply $ \dfrac{3x}{4} $ by $ \dfrac{8}{9} $ to get $ \dfrac{ 24x }{ 36 } $.

Step 1: Multiply numerators and denominators.

Step 2: Simplify numerator and denominator.

$$ \begin{aligned} \frac{3x}{4} \cdot \frac{8}{9} \xlongequal{\text{Step 1}} \frac{ 3x \cdot 8 }{ 4 \cdot 9 } \xlongequal{\text{Step 2}} \frac{ 24x }{ 36 } \end{aligned} $$

Subtract $ \dfrac{24x}{36} $ from $ 1 $ to get $ \dfrac{ \color{purple}{ -24x+36 } }{ 36 }$.

Step 1: Write $ 1 $ 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 $\color{blue}{ 36 }$.

$$ \begin{aligned} 1- \frac{24x}{36} & \xlongequal{\text{Step 1}} \frac{1}{\color{red}{1}} - \frac{24x}{36} = \frac{ 1 \cdot \color{blue}{ 36 }}{ 1 \cdot \color{blue}{ 36 }} - \frac{ 24x }{ 36 } = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ 36 } }{ 36 } - \frac{ \color{purple}{ 24x } }{ 36 }=\frac{ \color{purple}{ -24x+36 } }{ 36 } \end{aligned} $$