(9b+4)(5b-15)=0

Solution for (9b+4)(5b-15)=0 equation:

(9b+4)(5b-15)=0

We multiply parentheses ..

(+45b^2-135b+20b-60)=0

We get rid of parentheses

45b^2-135b+20b-60=0

We add all the numbers together, and all the variables

45b^2-115b-60=0

a = 45; b = -115; c = -60;
Δ = b2-4ac
Δ = -1152-4·45·(-60)
Δ = 24025
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{24025}=155$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-115)-155}{2*45}=\frac{-40}{90}
=-4/9
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-115)+155}{2*45}=\frac{270}{90}
=3
$