300=n^2-20n

Solution for 300=n^2-20n equation:

300=n^2-20n

We move all terms to the left:

300-(n^2-20n)=0

We get rid of parentheses

-n^2+20n+300=0

We add all the numbers together, and all the variables

-1n^2+20n+300=0

a = -1; b = 20; c = +300;
Δ = b2-4ac
Δ = 202-4·(-1)·300
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-40}{2*-1}=\frac{-60}{-2}
=+30
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+40}{2*-1}=\frac{20}{-2}
=-10
$