Subtract $n$ from $ \dfrac{n^2}{n} $ to get $ \dfrac{ \color{purple}{ 0 } }{ n }$.

Step 1: Write $ n $ 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 second fraction by $\color{blue}{n}$.

$$ \begin{aligned} \frac{n^2}{n} -n & \xlongequal{\text{Step 1}} \frac{n^2}{n} - \frac{n}{\color{red}{1}} = \frac{ n^2 }{ n } - \frac{ n \cdot \color{blue}{ n }}{ 1 \cdot \color{blue}{ n }} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ n^2 } }{ n } - \frac{ \color{purple}{ n^2 } }{ n }=\frac{ \color{purple}{ 0 } }{ n } \end{aligned} $$

Add $0$ and $ \dfrac{5}{n} $ to get $ \dfrac{ \color{purple}{ 5 } }{ n }$.

Step 1: Write $ 0 $ 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 first fraction by $\color{blue}{ n }$.

$$ \begin{aligned} 0+ \frac{5}{n} & \xlongequal{\text{Step 1}} \frac{0}{\color{red}{1}} + \frac{5}{n} = \frac{ 0 \cdot \color{blue}{ n }}{ 1 \cdot \color{blue}{ n }} + \frac{ 5 }{ n } = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ 0n } }{ n } + \frac{ \color{purple}{ 5 } }{ n }=\frac{ \color{purple}{ 5 } }{ n } \end{aligned} $$