0.3x+0.3x(x+10)=300

Solution for 0.3x+0.3x(x+10)=300 equation:

0.3x+0.3x(x+10)=300

We move all terms to the left:

0.3x+0.3x(x+10)-(300)=0

We multiply parentheses

0x^2+0.3x+0x-300=0

We add all the numbers together, and all the variables

x^2+1.3x-300=0

a = 1; b = 1.3; c = -300;
Δ = b2-4ac
Δ = 1.32-4·1·(-300)
Δ = 1201.69
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{-(1.3)-\sqrt{1201.69}}{2*1}=\frac{-1.3-\sqrt{1201.69}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1.3)+\sqrt{1201.69}}{2*1}=\frac{-1.3+\sqrt{1201.69}}{2}
$