0=80x-0.2x^2

Solution for 0=80x-0.2x^2 equation:

0=80x-0.2x^2

We move all terms to the left:

0-(80x-0.2x^2)=0

We add all the numbers together, and all the variables

-(80x-0.2x^2)=0

We get rid of parentheses

0.2x^2-80x=0

a = 0.2; b = -80; c = 0;
Δ = b2-4ac
Δ = -802-4·0.2·0
Δ = 6400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{6400}=80$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-80)-80}{2*0.2}=\frac{0}{0.4}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-80)+80}{2*0.2}=\frac{160}{0.4}
=400
$