Y=-0.04x2+8.3x

Solution for Y=-0.04x2+8.3x equation:

=-0.04Y^2+8.3Y

We move all terms to the left:

-(-0.04Y^2+8.3Y)=0

We get rid of parentheses

0.04Y^2-8.3Y=0

a = 0.04; b = -8.3; c = 0;
Δ = b2-4ac
Δ = -8.32-4·0.04·0
Δ = 68.89
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8.3)-\sqrt{68.89}}{2*0.04}=\frac{8.3-\sqrt{68.89}}{0.08}
$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8.3)+\sqrt{68.89}}{2*0.04}=\frac{8.3+\sqrt{68.89}}{0.08}
$