.20=-0.2n^2+7.2n+1.5

Solution for .20=-0.2n^2+7.2n+1.5 equation:

.20=-0.2n^2+7.2n+1.5

We move all terms to the left:

.20-(-0.2n^2+7.2n+1.5)=0

We add all the numbers together, and all the variables

-(-0.2n^2+7.2n+1.5)+0.2=0

We get rid of parentheses

0.2n^2-7.2n-1.5+0.2=0

We add all the numbers together, and all the variables

0.2n^2-7.2n-1.3=0

a = 0.2; b = -7.2; c = -1.3;
Δ = b2-4ac
Δ = -7.22-4·0.2·(-1.3)
Δ = 52.88
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7.2)-\sqrt{52.88}}{2*0.2}=\frac{7.2-\sqrt{52.88}}{0.4}
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7.2)+\sqrt{52.88}}{2*0.2}=\frac{7.2+\sqrt{52.88}}{0.4}
$