200=1.2x+0.06x^2

Solution for 200=1.2x+0.06x^2 equation:

200=1.2x+0.06x^2

We move all terms to the left:

200-(1.2x+0.06x^2)=0

We get rid of parentheses

-0.06x^2-1.2x+200=0

a = -0.06; b = -1.2; c = +200;
Δ = b2-4ac
Δ = -1.22-4·(-0.06)·200
Δ = 49.44
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{49.44}}{2*-0.06}=\frac{1.2-\sqrt{49.44}}{-0.12}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1.2)+\sqrt{49.44}}{2*-0.06}=\frac{1.2+\sqrt{49.44}}{-0.12}
$