Subtract $ \dfrac{-5}{6} $ from $ \dfrac{2}{5} $ to get $ \dfrac{ \color{purple}{ 37 } }{ 30 }$.

To subtract fractions they must have the same denominator.
We can create a common denominator by multiplying the first fraction by $ \color{blue}{ 6 }$ and the second by $\color{blue}{ 5 }$.

$$ \begin{aligned} \frac{2}{5} - \frac{-5}{6} & = \frac{ 2 \cdot \color{blue}{ 6 }}{ 5 \cdot \color{blue}{ 6 }} - \frac{ \left( -5 \right) \cdot \color{blue}{ 5 }}{ 6 \cdot \color{blue}{ 5 }} = \\[1ex] &=\frac{ \color{purple}{ 12 } }{ 30 } - \frac{ \color{purple}{ -25 } }{ 30 }=\frac{ \color{purple}{ 37 } }{ 30 } \end{aligned} $$