Use the distributive property.

Multiply $ \dfrac{2}{9} $ by $ s $ to get $ \dfrac{ 2s }{ 9 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{2}{9} \cdot s & \xlongequal{\text{Step 1}} \frac{2}{9} \cdot \frac{s}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 2 \cdot s }{ 9 \cdot 1 } \xlongequal{\text{Step 3}} \frac{ 2s }{ 9 } \end{aligned} $$

Add $ \dfrac{2s}{9} $ and $ 4 $ to get $ \dfrac{ \color{purple}{ 2s+36 } }{ 9 }$.

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

Step 2: To add raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the second fraction by $\color{blue}{9}$.

$$ \begin{aligned} \frac{2s}{9} +4 & \xlongequal{\text{Step 1}} \frac{2s}{9} + \frac{4}{\color{red}{1}} = \frac{ 2s }{ 9 } + \frac{ 4 \cdot \color{blue}{ 9 }}{ 1 \cdot \color{blue}{ 9 }} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ 2s } }{ 9 } + \frac{ \color{purple}{ 36 } }{ 9 }=\frac{ \color{purple}{ 2s+36 } }{ 9 } \end{aligned} $$

Multiply $ \dfrac{2s+36}{9} $ by $ t $ to get $ \dfrac{ 2st+36t }{ 9 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{2s+36}{9} \cdot t & \xlongequal{\text{Step 1}} \frac{2s+36}{9} \cdot \frac{t}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ \left( 2s+36 \right) \cdot t }{ 9 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 2st+36t }{ 9 } \end{aligned} $$

Add $ \dfrac{2st+36t}{9} $ and $ 5 $ to get $ \dfrac{ \color{purple}{ 2st+36t+45 } }{ 9 }$.

Step 1: Write $ 5 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: To add raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the second fraction by $\color{blue}{9}$.

$$ \begin{aligned} \frac{2st+36t}{9} +5 & \xlongequal{\text{Step 1}} \frac{2st+36t}{9} + \frac{5}{\color{red}{1}} = \frac{ 2st+36t }{ 9 } + \frac{ 5 \cdot \color{blue}{ 9 }}{ 1 \cdot \color{blue}{ 9 }} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ 2st+36t } }{ 9 } + \frac{ \color{purple}{ 45 } }{ 9 }=\frac{ \color{purple}{ 2st+36t+45 } }{ 9 } \end{aligned} $$