0.4=3x-x^2

Solution for 0.4=3x-x^2 equation:

0.4=3x-x^2

We move all terms to the left:

0.4-(3x-x^2)=0

We get rid of parentheses

x^2-3x+0.4=0

a = 1; b = -3; c = +0.4;
Δ = b2-4ac
Δ = -32-4·1·0.4
Δ = 7.4
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{-(-3)-\sqrt{7.4}}{2*1}=\frac{3-\sqrt{7.4}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-3)+\sqrt{7.4}}{2*1}=\frac{3+\sqrt{7.4}}{2}
$