0=-6b^2+12b+90

Solution for 0=-6b^2+12b+90 equation:

0=-6b^2+12b+90

We move all terms to the left:

0-(-6b^2+12b+90)=0

We add all the numbers together, and all the variables

-(-6b^2+12b+90)=0

We get rid of parentheses

6b^2-12b-90=0

a = 6; b = -12; c = -90;
Δ = b2-4ac
Δ = -122-4·6·(-90)
Δ = 2304
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2304}=48$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-48}{2*6}=\frac{-36}{12}
=-3
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+48}{2*6}=\frac{60}{12}
=5
$