160=20.x+5.x^2

Solution for 160=20.x+5.x^2 equation:

160=20.x+5.x^2

We move all terms to the left:

160-(20.x+5.x^2)=0

We get rid of parentheses

-5.x^2-20.x+160=0

We add all the numbers together, and all the variables

-5x^2-20x+160=0

a = -5; b = -20; c = +160;
Δ = b2-4ac
Δ = -202-4·(-5)·160
Δ = 3600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3600}=60$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-60}{2*-5}=\frac{-40}{-10}
=+4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+60}{2*-5}=\frac{80}{-10}
=-8
$