-8b(5b-10)+5=-15

Solution for -8b(5b-10)+5=-15 equation:

-8b(5b-10)+5=-15

We move all terms to the left:

-8b(5b-10)+5-(-15)=0

We add all the numbers together, and all the variables

-8b(5b-10)+20=0

We multiply parentheses

-40b^2+80b+20=0

a = -40; b = 80; c = +20;
Δ = b2-4ac
Δ = 802-4·(-40)·20
Δ = 9600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{9600}=\sqrt{1600*6}=\sqrt{1600}*\sqrt{6}=40\sqrt{6}$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(80)-40\sqrt{6}}{2*-40}=\frac{-80-40\sqrt{6}}{-80}
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(80)+40\sqrt{6}}{2*-40}=\frac{-80+40\sqrt{6}}{-80}
$