-8b(5b-10)+5=-115

Solution for -8b(5b-10)+5=-115 equation:

-8b(5b-10)+5=-115

We move all terms to the left:

-8b(5b-10)+5-(-115)=0

We add all the numbers together, and all the variables

-8b(5b-10)+120=0

We multiply parentheses

-40b^2+80b+120=0

a = -40; b = 80; c = +120;
Δ = b2-4ac
Δ = 802-4·(-40)·120
Δ = 25600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{25600}=160$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(80)-160}{2*-40}=\frac{-240}{-80}
=+3
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(80)+160}{2*-40}=\frac{80}{-80}
=-1
$