Add $ \dfrac{3}{4} $ and $ \dfrac{5}{6} $ to get $ \dfrac{ \color{purple}{ 19 } }{ 12 }$.

To add fractions they must have the same denominator.
We can create a common denominator by multiplying the first fraction by $ \color{blue}{ 3 }$ and the second by $\color{blue}{ 2 }$.

$$ \begin{aligned} \frac{3}{4} + \frac{5}{6} & = \frac{ 3 \cdot \color{blue}{ 3 }}{ 4 \cdot \color{blue}{ 3 }} + \frac{ 5 \cdot \color{blue}{ 2 }}{ 6 \cdot \color{blue}{ 2 }} = \\[1ex] &=\frac{ \color{purple}{ 9 } }{ 12 } + \frac{ \color{purple}{ 10 } }{ 12 }=\frac{ \color{purple}{ 19 } }{ 12 } \end{aligned} $$