The root of polynomial $ p(x) $ is:
$$ \begin{aligned}x &= -\dfrac{ 3 }{ 4 } \end{aligned} $$Step 1:
Combine like terms:
$$ 4x+ \color{blue}{6} \color{blue}{-3} = 4x+ \color{blue}{3} $$Step 2:
$$ \begin{aligned} 4x+3 & = 0 \\[1 em] 4 \cdot x & = -3 \\[1 em] x & = - \frac{ 3 }{ 4 } \end{aligned} $$