(30+3x)(45-5x)=0

Solution for (30+3x)(45-5x)=0 equation:

(30+3x)(45-5x)=0

We add all the numbers together, and all the variables

(3x+30)(-5x+45)=0

We multiply parentheses ..

(-15x^2+135x-150x+1350)=0

We get rid of parentheses

-15x^2+135x-150x+1350=0

We add all the numbers together, and all the variables

-15x^2-15x+1350=0

a = -15; b = -15; c = +1350;
Δ = b2-4ac
Δ = -152-4·(-15)·1350
Δ = 81225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81225}=285$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-285}{2*-15}=\frac{-270}{-30}
=+9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+285}{2*-15}=\frac{300}{-30}
=-10
$