Add $ \dfrac{x-8}{15} $ and $ \dfrac{1}{x} $ to get $ \dfrac{ \color{purple}{ x^2-8x+15 } }{ 15x }$.

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}{ x }$ and the second by $\color{blue}{ 15 }$.

$$ \begin{aligned} \frac{x-8}{15} + \frac{1}{x} & = \frac{ \left( x-8 \right) \cdot \color{blue}{ x }}{ 15 \cdot \color{blue}{ x }} + \frac{ 1 \cdot \color{blue}{ 15 }}{ x \cdot \color{blue}{ 15 }} = \\[1ex] &=\frac{ \color{purple}{ x^2-8x } }{ 15x } + \frac{ \color{purple}{ 15 } }{ 15x }=\frac{ \color{purple}{ x^2-8x+15 } }{ 15x } \end{aligned} $$