20x+(4-X)*28x=4*20

Solution for 20x+(4-X)*28x=4*20 equation:

20x+(4-x)*28x=4*20

We move all terms to the left:

20x+(4-x)*28x-(4*20)=0

We add all the numbers together, and all the variables

20x+(-1x+4)*28x-80=0

We multiply parentheses

-28x^2+20x+112x-80=0

We add all the numbers together, and all the variables

-28x^2+132x-80=0

a = -28; b = 132; c = -80;
Δ = b2-4ac
Δ = 1322-4·(-28)·(-80)
Δ = 8464
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8464}=92$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(132)-92}{2*-28}=\frac{-224}{-56}
=+4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(132)+92}{2*-28}=\frac{-40}{-56}
=5/7
$