12=10x-0.001x2

Solution for 12=10x-0.001x2 equation:

12=10x-0.001x^2

We move all terms to the left:

12-(10x-0.001x^2)=0

We get rid of parentheses

0.001x^2-10x+12=0

a = 0.001; b = -10; c = +12;
Δ = b2-4ac
Δ = -102-4·0.001·12
Δ = 99.952
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{-(-10)-\sqrt{99.952}}{2*0.001}=\frac{10-\sqrt{99.952}}{0.002}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+\sqrt{99.952}}{2*0.001}=\frac{10+\sqrt{99.952}}{0.002}
$