F(x)=20x+6x-x^2

Solution for F(x)=20x+6x-x^2 equation:

(F)=20F+6F-F^2

We move all terms to the left:

(F)-(20F+6F-F^2)=0

We get rid of parentheses

F^2-20F-6F+F=0

We add all the numbers together, and all the variables

F^2-25F=0

a = 1; b = -25; c = 0;
Δ = b2-4ac
Δ = -252-4·1·0
Δ = 625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{625}=25$
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-25)-25}{2*1}=\frac{0}{2}
=0
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-25)+25}{2*1}=\frac{50}{2}
=25
$