0.03y(4000-y)-9y=0

Solution for 0.03y(4000-y)-9y=0 equation:

0.03y(4000-y)-9y=0

We add all the numbers together, and all the variables

0.03y(-1y+4000)-9y=0

We add all the numbers together, and all the variables

-9y+0.03y(-1y+4000)=0

We multiply parentheses

0y^2-9y+0y=0

We add all the numbers together, and all the variables

y^2-8y=0

a = 1; b = -8; c = 0;
Δ = b2-4ac
Δ = -82-4·1·0
Δ = 64
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{64}=8$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-8}{2*1}=\frac{0}{2}
=0
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+8}{2*1}=\frac{16}{2}
=8
$