C(x)=0.06x-0.0002x^2

Solution for C(x)=0.06x-0.0002x^2 equation:

(C)=0.06C-0.0002C^2

We move all terms to the left:

(C)-(0.06C-0.0002C^2)=0

We get rid of parentheses

0.0002C^2-0.06C+C=0

We add all the numbers together, and all the variables

0.0002C^2+0.94C=0

a = 0.0002; b = 0.94; c = 0;
Δ = b2-4ac
Δ = 0.942-4·0.0002·0
Δ = 0.8836
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$C_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$C_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0.94)-\sqrt{0.8836}}{2*0.0002}=\frac{-0.94-\sqrt{0.8836}}{0.0004}
$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0.94)+\sqrt{0.8836}}{2*0.0002}=\frac{-0.94+\sqrt{0.8836}}{0.0004}
$