G=0.3n-0.2n^2

Solution for G=0.3n-0.2n^2 equation:

=0.3G-0.2G^2

We move all terms to the left:

-(0.3G-0.2G^2)=0

We get rid of parentheses

0.2G^2-0.3G=0

a = 0.2; b = -0.3; c = 0;
Δ = b2-4ac
Δ = -0.32-4·0.2·0
Δ = 0.09
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$G_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$G_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$G_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-0.3)-\sqrt{0.09}}{2*0.2}=\frac{0.3-\sqrt{0.09}}{0.4}
$
$G_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.3)+\sqrt{0.09}}{2*0.2}=\frac{0.3+\sqrt{0.09}}{0.4}
$