C(x)=0.2x^2-36x+18.689

Solution for C(x)=0.2x^2-36x+18.689 equation:

(C)=0.2C^2-36C+18.689

We move all terms to the left:

(C)-(0.2C^2-36C+18.689)=0

We get rid of parentheses

-0.2C^2+C+36C-18.689=0

We add all the numbers together, and all the variables

-0.2C^2+37C-18.689=0

a = -0.2; b = 37; c = -18.689;
Δ = b2-4ac
Δ = 372-4·(-0.2)·(-18.689)
Δ = 1354.0488
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{-(37)-\sqrt{1354.0488}}{2*-0.2}=\frac{-37-\sqrt{1354.0488}}{-0.4}
$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(37)+\sqrt{1354.0488}}{2*-0.2}=\frac{-37+\sqrt{1354.0488}}{-0.4}
$