(0.30-x)(0.40-x)=0

Solution for (0.30-x)(0.40-x)=0 equation:

(0.30-x)(0.40-x)=0

We add all the numbers together, and all the variables

(-1x+0.3)(-1x+0.4)=0

We multiply parentheses ..

(+x^2-0.4x-0.3x+0.12)=0

We get rid of parentheses

x^2-0.4x-0.3x+0.12=0

We add all the numbers together, and all the variables

x^2-0.7x+0.12=0

a = 1; b = -0.7; c = +0.12;
Δ = b2-4ac
Δ = -0.72-4·1·0.12
Δ = 0.01
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{-(-0.7)-\sqrt{0.01}}{2*1}=\frac{0.7-\sqrt{0.01}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.7)+\sqrt{0.01}}{2*1}=\frac{0.7+\sqrt{0.01}}{2}
$