A=4x2-280x+4800

Solution for A=4x2-280x+4800 equation:

=4A^2-280A+4800

We move all terms to the left:

-(4A^2-280A+4800)=0

We get rid of parentheses

-4A^2+280A-4800=0

a = -4; b = 280; c = -4800;
Δ = b2-4ac
Δ = 2802-4·(-4)·(-4800)
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(280)-40}{2*-4}=\frac{-320}{-8}
=+40
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(280)+40}{2*-4}=\frac{-240}{-8}
=+30
$