0.06x+0.04x(x+7000)=680

Solution for 0.06x+0.04x(x+7000)=680 equation:

0.06x+0.04x(x+7000)=680

We move all terms to the left:

0.06x+0.04x(x+7000)-(680)=0

We multiply parentheses

0x^2+0.06x+0x-680=0

We add all the numbers together, and all the variables

x^2+1.06x-680=0

a = 1; b = 1.06; c = -680;
Δ = b2-4ac
Δ = 1.062-4·1·(-680)
Δ = 2721.1236
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{-(1.06)-\sqrt{2721.1236}}{2*1}=\frac{-1.06-\sqrt{2721.1236}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1.06)+\sqrt{2721.1236}}{2*1}=\frac{-1.06+\sqrt{2721.1236}}{2}
$