Subtract $ \dfrac{7}{5} $ from $ \dfrac{-i}{2} $ to get $ \dfrac{ \color{purple}{ -5i-14 } }{ 10 }$.

To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $ \color{blue}{ 5 }$ and the second by $\color{blue}{ 2 }$.

$$ \begin{aligned} \frac{-i}{2} - \frac{7}{5} & = \frac{ \left( -i \right) \cdot \color{blue}{ 5 }}{ 2 \cdot \color{blue}{ 5 }} - \frac{ 7 \cdot \color{blue}{ 2 }}{ 5 \cdot \color{blue}{ 2 }} = \\[1ex] &=\frac{ \color{purple}{ -5i } }{ 10 } - \frac{ \color{purple}{ 14 } }{ 10 }=\frac{ \color{purple}{ -5i-14 } }{ 10 } \end{aligned} $$

Subtract $ \dfrac{2+5i}{2} $ from $ \dfrac{-5i-14}{10} $ to get $ \dfrac{ \color{purple}{ -30i-24 } }{ 10 }$.

To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the second fraction by $\color{blue}{5}$.

$$ \begin{aligned} \frac{-5i-14}{10} - \frac{2+5i}{2} & = \frac{ -5i-14 }{ 10 } - \frac{ \left( 2+5i \right) \cdot \color{blue}{ 5 }}{ 2 \cdot \color{blue}{ 5 }} = \\[1ex] &=\frac{ \color{purple}{ -5i-14 } }{ 10 } - \frac{ \color{purple}{ 10+25i } }{ 10 }=\frac{ \color{purple}{ -5i-14 - \left( 10+25i \right) } }{ 10 } = \\[1ex] &=\frac{ \color{purple}{ -30i-24 } }{ 10 } \end{aligned} $$