Multiply $20$ by $ \dfrac{a}{16} $ to get $ \dfrac{ 20a }{ 16 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} 20 \cdot \frac{a}{16} & \xlongequal{\text{Step 1}} \frac{20}{\color{red}{1}} \cdot \frac{a}{16} \xlongequal{\text{Step 2}} \frac{ 20 \cdot a }{ 1 \cdot 16 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 20a }{ 16 } \end{aligned} $$

Divide both the top and bottom numbers by $ \color{orangered}{ 8 } $.

Multiply $20$ by $ \dfrac{a}{16} $ to get $ \dfrac{ 20a }{ 16 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} 20 \cdot \frac{a}{16} & \xlongequal{\text{Step 1}} \frac{20}{\color{red}{1}} \cdot \frac{a}{16} \xlongequal{\text{Step 2}} \frac{ 20 \cdot a }{ 1 \cdot 16 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 20a }{ 16 } \end{aligned} $$

Add $ \dfrac{20a}{16} $ and $ \dfrac{2}{3} $ to get $ \dfrac{ \color{purple}{ 60a+32 } }{ 48 }$.

To add raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $ \color{blue}{ 3 }$ and the second by $\color{blue}{ 16 }$.

$$ \begin{aligned} \frac{20a}{16} + \frac{2}{3} & = \frac{ 20a \cdot \color{blue}{ 3 }}{ 16 \cdot \color{blue}{ 3 }} + \frac{ 2 \cdot \color{blue}{ 16 }}{ 3 \cdot \color{blue}{ 16 }} = \\[1ex] &=\frac{ \color{purple}{ 60a } }{ 48 } + \frac{ \color{purple}{ 32 } }{ 48 }=\frac{ \color{purple}{ 60a+32 } }{ 48 } \end{aligned} $$