The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0\\[1 em]x_2 &= -\frac{ 32 }{ 25 } \end{aligned} $$Step 1:
Factor out $ \color{blue}{ x^3 }$ from $ 25x^4+32x^3 $ and solve two separate equations:
$$ \begin{aligned} 25x^4+32x^3 & = 0\\[1 em] \color{blue}{ x^3 }\cdot ( 25x+32 ) & = 0 \\[1 em] \color{blue}{ x^3 = 0} ~~ \text{or} ~~ 25x+32 & = 0 \end{aligned} $$One solution is $ \color{blue}{ x = 0 } $. Use second equation to find the remaining roots.
Step 2:
To find the last zero, solve equation $ 25x+32 = 0 $
$$ \begin{aligned} 25x+32 & = 0 \\[1 em] 25 \cdot x & = -32 \\[1 em] x & = - \frac{ 32 }{ 25 } \end{aligned} $$