7=0.003x^2+0.001x

Solution for 7=0.003x^2+0.001x equation:

7=0.003x^2+0.001x

We move all terms to the left:

7-(0.003x^2+0.001x)=0

We get rid of parentheses

-0.003x^2-0.001x+7=0

a = -0.003; b = -0.001; c = +7;
Δ = b2-4ac
Δ = -0.0012-4·(-0.003)·7
Δ = 0.084001
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{-(-0.001)-\sqrt{0.084001}}{2*-0.003}=\frac{0.001-\sqrt{0.084001}}{-0.006}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.001)+\sqrt{0.084001}}{2*-0.003}=\frac{0.001+\sqrt{0.084001}}{-0.006}
$