(3x)(5x+20)=180

Solution for (3x)(5x+20)=180 equation:

(3x)(5x+20)=180

We move all terms to the left:

(3x)(5x+20)-(180)=0

We multiply parentheses

15x^2+60x-180=0

a = 15; b = 60; c = -180;
Δ = b2-4ac
Δ = 602-4·15·(-180)
Δ = 14400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{14400}=120$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(60)-120}{2*15}=\frac{-180}{30}
=-6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(60)+120}{2*15}=\frac{60}{30}
=2
$