$$-4y(y+7)(y+9) = 0$$
Answer
$$ \begin{matrix}y_1 = 0 & y_2 = -7 & y_3 = -9 \end{matrix} $$
Explanation
$$ \begin{aligned} -4y(y+7)(y+9) &= 0&& \text{simplify left side} \\[1 em]-(4y^2+28y)(y+9) &= 0&& \\[1 em]-(4y^3+36y^2+28y^2+252y) &= 0&& \\[1 em]-(4y^3+64y^2+252y) &= 0&& \\[1 em]-4y^3-64y^2-252y &= 0&& \\[1 em] \end{aligned} $$
In order to solve $ \color{blue}{ -4x^{3}-64x^{2}-252x = 0 } $, first we need to factor our $ x $.
$$ -4x^{3}-64x^{2}-252x = x \left( -4x^{2}-64x-252 \right) $$$ x = 0 $ is a root of multiplicity $ 1 $.
The remaining roots can be found by solving equation $ -4x^{2}-64x-252 = 0$.
$ -4x^{2}-64x-252 = 0 $ is a quadratic equation.
You can use step-by-step quadratic equation solver to see a detailed explanation on how to solve this equation.
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