The root of polynomial $ p(k) $ is:
$$ \begin{aligned}k &= \frac{ 24 }{ 11 } \end{aligned} $$Step 1:
Get rid of fractions by multipling equation by $ \color{blue}{ 2 } $.
$$ \begin{aligned} \frac{5}{2}k+3k-12 & = 0 ~~~ / \cdot \color{blue}{ 2 } \\[1 em] 5k+6k-24 & = 0 \end{aligned} $$Step 2:
Combine like terms:
$$ \color{blue}{5k} + \color{blue}{6k} -24 = \color{blue}{11k} -24 $$Step 3:
$$ \begin{aligned} 11k-24 & = 0 \\[1 em] 11 \cdot k & = 24 \\[1 em] k & = \frac{ 24 }{ 11 } \end{aligned} $$