C=0.25x2-80x+300

Solution for C=0.25x2-80x+300 equation:

=0.25C^2-80C+300

We move all terms to the left:

-(0.25C^2-80C+300)=0

We get rid of parentheses

-0.25C^2+80C-300=0

a = -0.25; b = 80; c = -300;
Δ = b2-4ac
Δ = 802-4·(-0.25)·(-300)
Δ = 6100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$C_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{6100}=\sqrt{100*61}=\sqrt{100}*\sqrt{61}=10\sqrt{61}$
$C_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(80)-10\sqrt{61}}{2*-0.25}=\frac{-80-10\sqrt{61}}{-0.5}
$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(80)+10\sqrt{61}}{2*-0.25}=\frac{-80+10\sqrt{61}}{-0.5}
$