Multiply $ \dfrac{3}{20} $ by $ i $ to get $ \dfrac{ 3i }{ 20 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

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

Add $ \dfrac{1}{20} $ and $ \dfrac{3i}{20} $ to get $ \dfrac{3i+1}{20} $.

To add expressions with the same denominators, we add the numerators and write the result over the common denominator.

$$ \begin{aligned} \frac{1}{20} + \frac{3i}{20} & = \frac{1}{\color{blue}{20}} + \frac{3i}{\color{blue}{20}} =\frac{ 1 + 3i }{ \color{blue}{ 20 }} = \\[1ex] &= \frac{3i+1}{20} \end{aligned} $$