115=100-8x+0.6x^2

Solution for 115=100-8x+0.6x^2 equation:

115=100-8x+0.6x^2

We move all terms to the left:

115-(100-8x+0.6x^2)=0

We get rid of parentheses

-0.6x^2+8x-100+115=0

We add all the numbers together, and all the variables

-0.6x^2+8x+15=0

a = -0.6; b = 8; c = +15;
Δ = b2-4ac
Δ = 82-4·(-0.6)·15
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-10}{2*-0.6}=\frac{-18}{-1.2}
=+15
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+10}{2*-0.6}=\frac{2}{-1.2}
=-1+0.8/1.2
$