3=0.2x^2+1.8x

Solution for 3=0.2x^2+1.8x equation:

3=0.2x^2+1.8x

We move all terms to the left:

3-(0.2x^2+1.8x)=0

We get rid of parentheses

-0.2x^2-1.8x+3=0

a = -0.2; b = -1.8; c = +3;
Δ = b2-4ac
Δ = -1.82-4·(-0.2)·3
Δ = 5.64
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{-(-1.8)-\sqrt{5.64}}{2*-0.2}=\frac{1.8-\sqrt{5.64}}{-0.4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1.8)+\sqrt{5.64}}{2*-0.2}=\frac{1.8+\sqrt{5.64}}{-0.4}
$