3l+3l(l-5)=135

Solution for 3l+3l(l-5)=135 equation:

3l+3l(l-5)=135

We move all terms to the left:

3l+3l(l-5)-(135)=0

We multiply parentheses

3l^2+3l-15l-135=0

We add all the numbers together, and all the variables

3l^2-12l-135=0

a = 3; b = -12; c = -135;
Δ = b2-4ac
Δ = -122-4·3·(-135)
Δ = 1764
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$l_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$l_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1764}=42$
$l_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-42}{2*3}=\frac{-30}{6}
=-5
$
$l_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+42}{2*3}=\frac{54}{6}
=9
$