250=1.2x+0.04x^2

Solution for 250=1.2x+0.04x^2 equation:

250=1.2x+0.04x^2

We move all terms to the left:

250-(1.2x+0.04x^2)=0

We get rid of parentheses

-0.04x^2-1.2x+250=0

a = -0.04; b = -1.2; c = +250;
Δ = b2-4ac
Δ = -1.22-4·(-0.04)·250
Δ = 41.44
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{-(-1.2)-\sqrt{41.44}}{2*-0.04}=\frac{1.2-\sqrt{41.44}}{-0.08}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1.2)+\sqrt{41.44}}{2*-0.04}=\frac{1.2+\sqrt{41.44}}{-0.08}
$