200=1.3x+.04x^2

Solution for 200=1.3x+.04x^2 equation:

200=1.3x+.04x^2

We move all terms to the left:

200-(1.3x+.04x^2)=0

We get rid of parentheses

-.04x^2-1.3x+200=0

We add all the numbers together, and all the variables

-0.04x^2-1.3x+200=0

a = -0.04; b = -1.3; c = +200;
Δ = b2-4ac
Δ = -1.32-4·(-0.04)·200
Δ = 33.69
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{-(-1.3)-\sqrt{33.69}}{2*-0.04}=\frac{1.3-\sqrt{33.69}}{-0.08}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1.3)+\sqrt{33.69}}{2*-0.04}=\frac{1.3+\sqrt{33.69}}{-0.08}
$