-80((x^2)-57.6x+320)=0

Solution for -80((x^2)-57.6x+320)=0 equation:

-80((x^2)-57.6x+320)=0

We multiply parentheses

-80x^2+4560x-25600=0

a = -80; b = 4560; c = -25600;
Δ = b2-4ac
Δ = 45602-4·(-80)·(-25600)
Δ = 12601600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{12601600}=\sqrt{6400*1969}=\sqrt{6400}*\sqrt{1969}=80\sqrt{1969}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4560)-80\sqrt{1969}}{2*-80}=\frac{-4560-80\sqrt{1969}}{-160}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4560)+80\sqrt{1969}}{2*-80}=\frac{-4560+80\sqrt{1969}}{-160}
$