4=-0,04x^2+0,6x+1,8

Solution for 4=-0,04x^2+0,6x+1,8 equation:

4=-0.04x^2+0.6x+1.8

We move all terms to the left:

4-(-0.04x^2+0.6x+1.8)=0

We get rid of parentheses

0.04x^2-0.6x-1.8+4=0

We add all the numbers together, and all the variables

0.04x^2-0.6x+2.2=0

a = 0.04; b = -0.6; c = +2.2;
Δ = b2-4ac
Δ = -0.62-4·0.04·2.2
Δ = 0.008
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-0.6)-\sqrt{0.008}}{2*0.04}=\frac{0.6-\sqrt{0.008}}{0.08}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.6)+\sqrt{0.008}}{2*0.04}=\frac{0.6+\sqrt{0.008}}{0.08}
$