300=80*x-5*x^2

Solution for 300=80*x-5*x^2 equation:

300=80x-5x^2

We move all terms to the left:

300-(80x-5x^2)=0

We get rid of parentheses

5x^2-80x+300=0

a = 5; b = -80; c = +300;
Δ = b2-4ac
Δ = -802-4·5·300
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-80)-20}{2*5}=\frac{60}{10}
=6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-80)+20}{2*5}=\frac{100}{10}
=10
$