-20=56n-12n^2

Solution for -20=56n-12n^2 equation:

-20=56n-12n^2

We move all terms to the left:

-20-(56n-12n^2)=0

We get rid of parentheses

12n^2-56n-20=0

a = 12; b = -56; c = -20;
Δ = b2-4ac
Δ = -562-4·12·(-20)
Δ = 4096
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4096}=64$
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-56)-64}{2*12}=\frac{-8}{24}
=-1/3
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-56)+64}{2*12}=\frac{120}{24}
=5
$